High-efficiency processes for destruction of contaminats

ABSTRACT

The present invention relates to novel ex situ processes for simple and economical destruction of air, water, and soil contaminants using naturally occurring microorganisms that are widely available in the environment. The processes utilize novel closed-loop recycle schemes which dramatically improve the efficiency, economics, and practicability of destruction of a wide variety of contaminants, especially VOCs and chloroethylenes, and particularly trichloroethylene (TCE). The processes may be applied on a batch or continuous basis to contaminated soil and groundwater, to contaminated effluents from a wide variety industrial operations, or to wherever such amenable contaminants are present. Certain contaminants, particularly chloroethylenes, are known to be difficult to biodegrade aerobically to non-toxic products without the employment of a primary substrate to induce cometabolic degradation. Ordinarily, practical and economical cometabolic degradation of these compounds via a primary substrate is not possible because direct metabolic degradation of the primary substrate itself competes with degradation of the target pollutants, thus rendering degradation of the target pollutants economically prohibitive. The processes of the present invention utilize novel closed-loop recycle schemes and separate primary substrate streams and contaminant streams into separate and discrete process cycles to achieve simple, practical, and economical degradation of target pollutants. Conventional wisdom indicates that these closed-loop recycle schemes should deplete the oxygen supply, causing loss of the aerobic microorganisms and process failure. However, the novel closed-loop recycle schemes of the present invention unexpectedly result in dramatically improved efficiencies and economics for degradation of a wide variety of pollutants, particularly chloroethylenes.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to novel ex situ processes forsimple and economical destruction of air, water, and land contaminants.

[0003] 2. Description of Related Art

[0004] Many industrial operations today utilize raw materials, solvents,and cleaners which result in the release of harmful pollutants into theenvironment. In addition, widespread use and improper disposal of toxicmaterials in the past have resulted in contamination of many soils andsubsurface aquifers with harmful pollutants, particularly chlorinatedaliphatic hydrocarbons (Council on Environmental Quality; U.S.Environmental Protection Agency, 1981). The National Priority List ofthe USEPA lists TCE as one of the most frequently reported contaminantsat hazardous waste sites. In rural areas of the U.S., much of thedrinking water supply is provided by groundwater. TCE is one of the mostprevalent groundwater contaminants (Westrick et al. 1984; Lenhard et al.1995), and due to the serious health threat these contaminatedgroundwaters pose, remedial action of such areas are of major concern.Traditional clean-up methods for contaminated water includeair-stripping or air-stripping followed by granulated-activated carbon(GAC) adsorption. In either case, the contaminants are only transferredfrom one medium to another and must still be dealt with. In addition,traditional clean-up methods are often economically prohibitive due tothe low concentrations of the contaminants. In contrast, biodegradationprocesses can convert toxic pollutants to non-toxic products such ascarbon dioxide and water and are generally more economical thantraditional clean up methods at low contaminant concentrations.

[0005] In industrial operations, tightening regulations are requiringmore stringent controls on emissions and disposal, and chemical hygienerequirements are forcing the use of higher air volumes to provide workersafety, which results in high-volume, low-concentration contaminated airstreams. Such contaminated air streams may be diluted to the point thattraditional technologies, such as wet scrubbing, thermal oxidation, airstripping, or carbon adsorption may be either ineffective or too costly.Such dilute applications are well suited to biodegradation processes,which utilize microorganisms attached to natural or synthetic packing toactually biodegrade the target pollutants to non-toxic products ratherthan simply transfer them from one medium to another. Usingbiodegradation processes, contaminated streams are passed throughpacking containing microorganisms which degrade or mineralize thepollutants into harmless compounds such as carbon dioxide, salts, andwater. In many cases, biodegradation processes provide cost-effective,environmentally friendly alternatives to traditional pollution controlor remediation technologies.

[0006] The fate of chlorinated hydrocarbons, particularly TCE, is amajor concern of the Department of Defense (DoD). Numerous DoD sites inthe U.S. have been identified as having groundwater contaminated withchlorinated hydrocarbons as well as other hazardous organic compounds.The Army has prioritized “Solvents in Groundwater” as the fifth highestrequirement in the area of environmental cleanup research anddevelopment. At some DoD sites, contaminated groundwater is pumped toair strippers which remove the contaminants from the groundwater andtransfer them to an air stream. In many cases, these contaminated airstreams from the strippers are simply released to the environment. Inaddition, painting, coating, paint stripping, solvent degreasing, andother operations at DoD sites result in the release of streamscontaminated with TCE, methylene chloride, and other harmful VOCs(volatile organic compounds) and SVOCs (semi-volatile organic compounds)to the environment. Economical and practical processes are needed todegrade such contaminants to harmless by-products, either directly ingroundwater or wastewater, or in the air streams emitted to theenvironment from air stripping operations, from soil vapor extractionprocesses, or from other operations which release harmful pollutants.

[0007] Traditional contaminated groundwater clean-up methods includeair-stripping and/or granulated-activated carbon (GAC) adsorption.Generally, the contaminated groundwater is pumped to the surface andthen to the top of an air stripper, which usually consists of acylindrical column packed with material designed to maximizeliquid-to-air contact. The contaminated water flows down through thepacking by gravity as air is blown up through the column. The volatileorganic compounds are thus counter-currently stripped from the water andenter the air during transit through the stripper. In some cases, thiscontaminated air stream is then blown through an activated carbon filterdesigned for removal of the particular contaminants in question.However, the contaminants are not destroyed. They are simply held andconcentrated within the carbon filter. At some point in time the carbonfilter becomes saturated with contaminants, and then the contaminantsbegin to pass through the filter to the environment. At this time, it isnecessary to replace the contaminated carbon with fresh carbon and toeither dispose of the contaminated carbon or to send it to a vendor forregeneration, both of which are costly and inconvenient operations. Insome cases, the groundwater may be pumped directly through carbonfilters without first air stripping. In other cases, the groundwater isair stripped, the air from the air strippers is emitted to theenvironment, and the water effluents from the air strippers are passedthrough carbon filters to remove less volatile compounds which may notbe removed by the strippers. Unlike carbon adsorption, biodegradationprocesses such as biofiltration can destroy the contaminants and offerpractical, cost-effective, and environmentally friendly alternatives.

[0008] Biofiltration technology is being developed as an economical andenvironmentally friendly solution for a variety of remediation andpollution control applications. Example applications include both pointand non-point source industrial emissions (regulated by the 1990Amendments to the Clean Air Act) as well as site remediation wastestreams generated by soil vapor extraction and air sparging systems.Biofiltration technology has been accepted in Europe for the last 50years for the control of odors. Within the last decade, the technologyis gradually being adopted in the U.S., and the application base isbroadening to include the control of volatile organic compounds.

[0009] In most biodegradation processes, the microorganisms actuallyconsume and derive food value from the target pollutants, and the wastestream can be passed continuously through the processes to achievecontinuous degradation of the target pollutants in the waste stream. Inother words, the microorganisms directly metabolize the pollutants as asource of food and growth. Such biodegradation processes willhereinafter be referred to as direct-metabolism processes. Pollutantscapable of being directly consumed (or metabolized) by microorganisms inbiodegradation processes include methyl ethyl ketone, methyl isobutylketone, butyl acetate, toluene, xylene, styrene, benzene, carbondisulfide, hydrogen sulfide, ammonia, and many others.

[0010] However, with certain pollutants, such as chlorinated aliphatichydrocarbons and in particular the chloroethylenes, naturally occurringmicroorganisms cannot directly consume and derive food value from thepollutants. In other words, the microorganisms cannot directlymetabolize the pollutants. In such cases, certain alternate carbon(food) sources, or primary substrates, can be supplied that themicroorganisms directly metabolize, and in so doing, the microorganismsthereby generate enzymes capable of degrading certain target pollutantsthat cannot be directly metabolized. In other words, the pollutantstargeted for destruction are indirectly degraded by enzymes generatedwhen the microorganisms directly metabolize another compound in aprocess known as cometabolism. Hereinafter, such biodegradationprocesses shall be referred to as cometabolism processes. The alternateor primary food sources that the microorganisms directly metabolize canthemselves also be pollutants or undesirable compounds such as toluene,or they can be relatively innocuous compounds such as glucose orpropane.

[0011] Pollutants amenable to aerobic biodegradation via directmetabolism are those in which a wide variety of naturally occurringmicroorganisms can consume directly as sources of food, whereaspollutants requiring cometabolism for aerobic biodegradation are thosein which the naturally occurring cannot consume directly as sources offood. Pollutants amenable to biodegradation via direct metabolisminclude a wide variety of organic compounds including alcohols, esters,ethers, ketones, aromatics, and alkanes, such as ethanol, butyl acetate,methyl tertiary butyl ether, methyl ethyl ketone, toluene, and propane,resectively, and other organic or non-organic compounds that may or maynot contain halogens, sulfur, or nitrogen, such as methylene chloride,carbon disulfide, hydrogen sulfide, or ammonia. Pollutants requiringcometabolism for degradation include certain halogenated organiccompounds, especially the chloroethylenes, such as tetrachloroethylene,trichloroethylene, dichloroethylenes, and vinyl chloride.

[0012] As will easily be appreciated by one skilled in the art, a directmetabolism process in accordance with the present invention isessentially a cometabolism process in accordance with the presentinvention except that the target contaminant cometabolic degradationstep is omitted and only the direct metabolic metabolism step exists.

[0013] Obviously it is impossible to list all pollutants amenable toaerobic biodegradation via direct metabolism and those pollutantsamenable to aerobic biodegradation via cometabolism. In fact, quiteoften there is no strict line of distinction between these two classesof pollutants, and some are amenable to aerobic biodegradation bothdirect metabolism and via cometabolism. Since direct metabolism is asimpler process, if a pollutant is amenable to aerobic biodegradationvia simple direct metabolism, then direct metabolism will generally bethe process of choice. On the other hand, if a pollutant is amenable toaerobic biodegradation via direct metabolism but the process isinefficient, then, generally speaking, aerobic biodegradation viacometabolism will be the process of choice.

[0014] Cometabolism processes are complicated by the fact that thetarget pollutants are not efficiently destroyed when the primary foodsources are also present because the primary food sources compete withdegradation of the target pollutants. In other words, when both thetarget pollutants and the primary food sources are present together, themicroorganisms consumption (or direct metabolism) of the primary foodsources greatly reduces degradation of the target pollutant throughcompetitive inhibition. However, the degradation efficiency of thetarget pollutants can be improved by periodically withholding theprimary food sources to allow the enzymes generated by direct metabolismof the primary food sources to degrade the target pollutants in theabsence of the primary food source, thereby eliminating the deleteriouseffects of competitive inhibition.

[0015] TCE and other chlorinated aliphatic compounds can becometabolically degraded by aerobic microorganisms if a primary carbonand energy source is available. Wilson and Wilson, 1985, firstdemonstrated aerobic degradation of TCE by soil samples amended withmethane gas. Propane (Fliermans et al. 1988; Wackett et al. 1989),ammonia (Arciero et al. 1989), phenol (Hopkins et al. 1993), and toluene(Nelson et al. 1987) oxidizing microorganisms have also been reported todegrade TCE. Remediation systems containing methane-oxidizing bacteria,methanotrophs, have shown notable promise and have been extensivelystudied for the removal of TCE from contaminated streams. Methanotrophicisolate and mixed-culture systems have been studied in detail on themicrocosm scale for determination of the optimum degradation environmentand for degradation pathway determination (Brusseau et al. 1990; Fox etal. 1990; Little et al. 1988; Oldenhuis et al. 1989; Tsien et al. 1989).Furthermore, reactor experiments have been conducted (Fennell et al.1993; Strandberg et al. 1989; Tschantz et al. 1995; Alvarez-Cohen andMcCarty, 1991), and several studies have been reported where aquiferconditions were simulated in which methanotrophic organisms under properstimulation degraded TCE (Semprini et al. 1990; Semprini et al. 1991;Wilson and Wilson, 1985). Methanotrophic systems continue to beinvestigated due to evidence that suggests that under the properoperating conditions, these methane-oxidizing microorganisms oftendegrade TCE at faster rates than other TCE degraders (Fennell et al.1993; Chang and Alvarez-Cohen, 1995). Propane has been shown tostimulate TCE degradation (Phelps et al., 1991), and greater degradationefficiencies have been observed by manipulating or pulsing the primarysubstrate (Lackey, et. al. 1993). The teachings of the publications inthis paragraph with regard to microorganism types and primary substratetypes are hereby incorporated by reference and are discussed later inmore detail, infra.

[0016] Several patents have been issued which teach microorganisms ormethods for biodegradation of chlorinated compounds, some of whichemploy primary substrates (or primary food sources) to inducedegradation of the target pollutants, including U.S. Pat. Nos.4,452,894; 4,477,570; 4,664,805; 4,713,343; 4,749,491; 4,853,334;4,859,594; 4,925,802; and 4,954,258; 5,079,166; and 5,543,317. Theteachings of these patents with regard to microorganism types andprimary substrate types are hereby incorporated by reference.

[0017] U.S. Pat. No. 4,452,894 teaches a microorganism compositioncapable of utilizing various halogenated aromatic compounds as solesources of carbon without the need for primary substrate inducers, butit does not teach or claim said utilization of chlorinated aliphaticcompounds, such as chloroethylenes, as sole carbon sources.

[0018] U.S. Pat. No. 4,477,570 teaches microorganism strains whichdegrade aromatic and halogenated aromatic compounds without primarysubstrates, but it makes no claim of degradation of chlorinatedaliphatic hydrocarbons.

[0019] U.S. Pat. No. 4,664,805 teaches bacteria strains and in situmethods for accelerating the degradation of various halogenated organicpollutants, particularly polyhalogenated biphenyls, by addition ofnon-indigenous microorganisms and chemical analogs to contaminatedenvironments. Careful balance of concentrations of the non-indigenousmicroorganisms, the indigenous microorganisms, and the chemical analog;competition between the indigenous and the non-indigenousmicroorganisms; and competition between the chemical analog and thehalogenated metabolic by-products for degradation by the indigenousmicroorganisms diminish the practicality and economic viability of thismethod, as demonstrated by the low contaminant degradation ratesobtained and long contact times required.

[0020] U.S. Pat. No. 4,713,343 teaches in situ methods for aerobicallydegrading halogenated aliphatic hydrocarbons in contaminated water bytreating the water with microorganisms, alkane gases, and oxygensources. The alkane gases are added to the contaminated water as carbonsources (primary food sources) to induce degradation of the targetpollutants through an enzymatic pathway. The alkane gas inducers arethus co-mingled with the target contaminants of the environment,resulting in competition between the inducer and the target contaminantsfor degradation by the microorganisms. As prior art teaches, suchco-mingling and competition between the inducer (primary food source)and target contaminants renders such methods cost prohibitive due to thelow target contaminant degradation rates resulting from competitiveinhibition of target contaminant degradation by degradation of theinducer. The low target contaminant degradation rates obtained using themethods taught in this patent are demonstrated by the long contact timesrequired to achieve degradation of the target contaminants.

[0021] U.S. Pat. No. 4,749,491 teaches an in situ method for stimulatingindigenous bacteria to degrade chlorinated hydrocarbons in water andsoil through the addition of nutrients and oxygen sources such ashydrogen peroxide without the use of inducers such as propane ormethane. Control of concentrations of the nutrients must be maintainedsuch that overgrowth of microorganisms does not cause plugging of thesubstrata. In the teachings of this patent, no record or proof isdemonstrated of the degradation of the subject contaminants by thesubject indigenous microorganisms. Rather, claim is made to the relativedegree of growth of unidentified microorganisms under aerobic laboratoryconditions in the presence of said contaminants, said nutrients, and airor hydrogen peroxide. This said relative degree of growth is determinedby subjective visual inspection of the relative degree of turbidity ofthe laboratory samples without identification of the microorganismspecies or any determination of its ability to degrade the subjectcontaminants.

[0022] U.S. Pat. No. 4,853,334 teaches a process using Pseudomonasfluorescens microorganisms to degrade haloaliphatic hydrocarbons, withor without carbon sources such as glucose or molasses as primarysubstrates to stimulate the bacteria to degrade the subjectcontaminants. However, the low degradation rates obtained and longcontact times required are cost prohibitive and impractical forcommercial applications. For example, only 2% of TCE present wasdegraded in 24 hours and only 13% of TCE present was degraded in 5 days.

[0023] U.S. Pat. No. 4,859,594 teaches microorganism strains and methodsfor genetically modifying, immobilizing, and utilizing said strains fordegrading chloroethanes, chlorophenols, and PCPs without the use ofprimary substrates to induce degradation of the subject contaminants.However, the teachings make no provision or claim of degradation ofchloroethylenes such as TCE. Furthermore, the genetically modifiedmicroorganisms are subject to competition by other microorganisms whichmay develop, thrive, and dominate when the subject biodegradation mediaare subjected to contaminants in the environment either incidentally orby choice other than those on which the said genetically modifiedorganisms are adapted to dominate and thrive. Such competition anddomination of alternate organisms which thrive on other contaminants canresult in loss of capacity or function of genetically modifiedbiodegradation media to degrade the contaminants they were adapted todegrade and intended to degrade.

[0024] U.S. Pat. No. 4,925,802 teaches a method for biodegradation ofhalogenated aliphatic hydrocarbons such as TCE by the addition of anaromatic amino acid primary substrate, in particular tryptophan, toinduce degradation of the subject contaminants through activation of anoxygenase enzymatic pathway. An alternate method involves a preliminarystep in which the microorganisms are first stimulated with the primarysubstrate to induce activation of the enzymes capable of degrading thesubject contaminants followed by addition of the said stimulatedmicroorganisms to the environment containing the subject contaminants,with or without additional inducer. However, with this method, presenceof the inducer is required to sustain microbial production of thecontaminant-degrading enzymes, and when the enzymes produced during thesaid preliminary stimulation step have been exhausted in thecontaminated environment through degrading the subject contaminants,additional inducer or additional pre-stimulated microorganisms would berequired to be added to the contaminated environment. Adding additionalinducer to the contaminated environment introduces the competitiveinhibition problems which exist with co-mingling of the inducer with thetarget contaminant. Adding additional pre-stimulated microorganisms tothe environment would require a dedicated process for production ofpre-stimulated microorganisms for repeated additions to the contaminatedenvironment until such time that satisfactory decontamination wasaccomplished, thus substantially increasing remediation costs. Inaddition, the said dedicated process for production of pre-stimulatedmicroorganisms would be required to be capable of completely consumingthe said inducer prior to introduction of the said pre-stimulatedmicroorganisms to the contaminated environment or the residual inducerwould be introduced as well into the environment, thus co-mingling theinducer with the subject contaminants and thus reducing the efficiencyand economic viability of the process.

[0025] U.S. Pat. No. 4,954,258 teaches improvements in prior art methodsfor alkane-induced, methanotrophic bacterial degradation of halogenatedaliphatic hydrocarbons in water (as in U.S. Pat No. 4,713,343, Wilson etal.) by substituting part or all of the alkane inducers with loweralkanols, in particular methanol. The subject patent teaches that thesubstituted alkanols provide an alternate carbon source for growth ofthe methanotrophic bacteria and that the alkanols do not substantiallybind with methane monooxygenase, the enzyme required for degradation ofthe halogenated aliphatic hydrocarbons, and thus the alkanols do notcompetitively inhibit degradation of the subject contaminants in the waythat alkanes do by competing for the methane monooxygenase. Rather, thealkanols are metabolized by methanol dehydrogenase. However, methanemonooxygenase is required for degradation of the halogenated aliphaticmicroorganisms. Therefore, when the methane monooxygenase supply isexhausted through degradation of the halogenated aliphatic hydrocarbons,methane or other stimulus must be added to the system to stimulateproduction of additional methane monooxygenase if degradation ofhalogenated hydrocarbons is to continue. The substituted methanolprovides a carbon source for growth of the methanotrophic bacteria butdoes not activate the methane monooxygenase enzyme required for theintended degradation of the halogenated aliphatic hydrocarbons. Thus, tocontinue degradation of the subject contaminants, adding additionalmethane or other methane monooxygenase inducing stimuli to thecontaminated environment or biodegradation media is required until suchtime that the environment or contaminated media is satisfactorilydecontaminated, which allows co-mingling of the methane monooxygenaseinducer with the subject contaminants and the associated competitiveinhibition problems which substantially reduce efficiency and economicviability. The low degradation rates demonstrated with use of the abovetaught method are cost prohibitive and preclude its economical use incommercial applications.

[0026] U.S. Pat. No. 5,079,166 teaches a method for degradation of TCEby treating TCE with genetically engineered and isolated microorganismscontaining a recombinant plasmid which contains toluene monooxygenasegenes. The microorganisms of the subject patent must have been treatedwith an inducer of the toluene monooxygenase genes. This method avoidsthe complications of competitive inhibition associated with co-minglingof the inducer with the contaminant, but the genetically engineeredmicroorganisms are not capable of sustaining degradation of TCE on theirown in the contaminated environment or degradation media. Newgenetically engineered microorganisms must be continually grown in aseparate controlled environment and continually added to thecontaminated environment until such time that decontamination iscomplete, or they must be continually added to a continuous ex situbioreactor process to sustain the degradation capacity of suchbioreactor until such time that operation of the bioreactor is no longerneeded or desired. Furthermore, the low degradation rates and longcontact times demonstrated by the methods of this invention as well asthe requirement for repeated separate-environment growth and addition ofthe genetically engineered microorganisms render the method costprohibitive for commercial operations, particularly for the case of exsitu bioreactor processes, requiring a period of hours for substantialdegradation TCE.

[0027] U.S. Pat. No. 5,543,317 teaches a bacterium capable of degradinghazardous chemicals, including chloroethylenes and TCE, without the useof a primary substrate to induce degradation of the subjectcontaminants. However, the said microorganisms are geneticallyengineered microorganisms, and therein exists several aforementioneddisadvantages with use of such organisms in natural environments. Suchdisadvantages can include additional processing costs, processcomplications, and process inefficiencies for the genetically engineeredmethods as described above concerning U.S. Pat. No. 5,079,166.Genetically engineered pure microorganism cultures generally are notcapable of sustaining their populations and thus their degradationefficiencies in the diverse contaminated environments encountered innature and therefore must be continually or periodically replenished dueto competing bacteria as well as competing substrates and contaminants.The low degradation rates (1.3 mg TCE/L/day) and long contact times(overnight incubation) demonstrated in this patent (U.S. Pat. No.5,543,317, supra) as well as the need for repeated separate controlledenvironment growth and addition of the genetically engineeredmicroorganisms render the method cost prohibitive for commercialoperations, particularly for the case of ex situ bioreactor processes,requiring an overnight period for substantial degradation of TCE.

[0028] Prior art teaches that ex situ biofilters and bioreactors areakin to microorganism zoos, with the microorganism cultures naturallyadapting, dominating, and maintaining themselves according the variouscompounds, food sources, and contaminants present or fed to thebiodegradation media. Biofilters and bioreactors can be inoculated withpure microorganism cultures, genetically engineered microorganismcultures, mixtures of various cultures, groundwater, soil sediments, orsewage sludge, but the inoculated cultures generally do not sustainthemselves in their original inoculated type and makeup in thebiodegradation media with the myriad of other indigenous microbes,substrates, and contaminants being fed to a biofilter or bioreactor fromsources open to the atmosphere and elements. There occurs adaptationsand changes within the microbial populations in the biodegradation mediato those cultures which best survive and thrive on what is available inthe natural environment or waste stream to be remediated or otherwisepurified of contaminants. Such natural environments generally include amyriad of indigenous microorganisms, contaminants, food sources, andcompounds other than those present in external controlled environmentsmanipulated to cause domination and purification of specific culturesfor degrading the compounds in the natural environment targeted fordetoxification. When such pure cultures are subjected to such naturalenvironments, either in situ or ex situ, changes in the microbialpopulations generally occur to favor those organisms which best thrivein the natural environments or in the bioreactor which is receiving thecontaminated stream from a natural environment or other operationexposed to the natural environment.

[0029] Indeed, there is no need for initial inoculation of biofilters orat all, since a myriad of naturally occurring microorganisms is presenteverywhere in the environment, and the waste streams containing thetarget contaminants fed to the ex situ biofilters or bioreactors fromthe natural environment already contain diverse wild type microorganismsthat have adapted to sustain themselves in the presence of the targetcontaminants, similarly to the way in which wild yeasts in theenvironment degrade sugars present in fruit into alcohol. The biofiltersor bioreactors function to immobilize, feed, and concentrate themicroorganism cultures which best degrade the target contaminants. Thus,when biofilter or bioreactor operations are initiated without an initialinoculum, the diverse wild type microorganisms present in thesurrounding environment and in the waste streams containing the targetcontaminants enter the biofilters or bioreactors and adapt, change,grow, and dominate to those cultures which best survive and thrive onthe contaminated streams, food sources, and nutrients present or passingthrough the biofilters or bioreactors. Pre-isolation and concentrationof microorganism cultures for initially inoculating biofilters orbioreactors may reduce start up time but is not necessary, sincechanges, adaptations, and dominance of certain cultures will occur evenin such isolated and inoculated cultures after operation begins and thebiofilters or bioreactors are subjected to complex mixtures of foodsources, contaminants, and microorganisms present in the naturalenvironment.

[0030] There appears no prior art in which the Applicants are aware ofthe ex situ cometabolic or direct metabolic processes of our inventionutilizing our novel closed-loop recycle schemes that (1) provideefficient and complete direct metabolism of primary substrates (foodsources), whether they themselves be pollutants or harmless compounds,without loss or venting of the primary substrates to the environment,(2) allow enzymatic degradation (cometabolism) of sorbed or residualtarget contaminants during feeding of the primary substrates to themicroorganisms without loss or venting of the primary substrates ortarget contaminants to the environment, (3) virtually precludeco-mingling of primary substrates with target contaminants and therebyachieve high target contaminant degradation efficiency, (4) utilizenaturally occurring microorganisms widely available in the environment,and (5) self-optimize to maintain the optimal microbial types andpopulations without the need for microorganism replenishment ormodification.

SUMMARY OF THE INVENTION

[0031] The present invention relates to novel, efficient, and economicalex situ processes utilizing closed-loop recycle schemes for cometabolicdegradation of chloroethylenes or other amenable target contaminantswhich alone are not easily or efficiently degraded by naturallyoccurring microorganisms and for direct metabolic degradation of a widevariety of other amenable contaminants. The processes of the presentinvention are not limited to utilization of any particular type ofmicroorganism and preferably utilize naturally occurring microorganismswhich are widely available in the surrounding environment and that areeasily obtainable from sources such as soil sediments, groundwater, orin the contaminated streams to be treated and that are widely taught inthe prior art, supra. Examples of such naturally occurringmicroorganisms which may be utilized in the processes of the presentinvention include those discussed in the prior art previouslyincorporated by reference.

[0032] The processes of the present invention for cometabolicdegradation utilize primary substrates (alternate food sources) toinduce enzymatic degradation (cometabolism) of target pollutants whichalone are not easily or efficiently biodegraded by such naturallyoccurring microorganisms, such as is the case with chloroethylenes,particularly TCE. Further, the processes of the present invention forcometabolic degradation are operated in a cyclical fashion such thatfeeding of the targeted waste or contaminated streams is separated fromfeeding of the primary substrate streams into separate and discreteprocess cycles to minimize or eliminate co-mingling of the primarysubstrate with the target contaminants. Most importantly, the processesof the present invention utilize novel closed-loop recycle schemes whichdramatically improve the efficiency, economics, and practicability ofsuch. During closed-loop recycle periods, the processes are virtuallyclosed to the outside environment with little or no net process flowsentering or leaving the processes. These novel closed-loop recycleschemes can be employed for direct metabolism of food sources, whetherthey be pollutants, undesirable compounds, or innocuous compounds,and/or for cometabolism of target contaminants incapable of directmetabolism. For contaminants requiring degradation by cometabolism, thenovel closed-loop recycle schemes can be employed not only during themicroorganism feeding periods (direct metabolism), but during the targetcontaminant degradation periods (cometabolism) as well. In addition,these novel closed-loop recycle schemes can be employed forhigh-efficiency destruction of a wide variety of pollutants andundesirable compounds that are capable of microbial degradation bydirect metabolism in a simplified process without a cometabolicdegradation cycle. In such simplified direct metabolism processes, thefood sources for the microorganisms are the pollutants targeted fordestruction and the processes are closed to outside environment exceptfor short periods to replenish microorganisms in the closed system withfresh air. The novel closed loop recycle schemes of the presentinvention may be used for treating either gas- or liquid-phase streamscontaining contaminants capable of direct metabolism and/or contaminantsrequiring cometabolism. The processes may be applied on a batch orcontinuous basis to contaminated soil and groundwater, to contaminatedeffluents from a wide variety industrial operations such as solventdegreasing, or to wherever amenable contaminants are present.

[0033] Chloroethylenes, particularly TCE, are known to be difficult tobiodegrade aerobically to non-toxic products without the employment of aprimary substrate to feed the microorganisms and thereby inducecometabolic degradation of the chloroethylenes through an enzymaticpathway. Ordinarily, practical and economical enzymatic degradation ofchloroethylenes via a primary substrate is not possible because directmetabolism (consumption) of the primary substrate itself competes withenzymatic cometabolic degradation of the target pollutants, thusrendering degradation of the target pollutant inefficient andeconomically prohibitive. In the processes of the present invention forcometabolic degradation, pulsing the primary substrate stream with thecontaminated stream, or in other words, alternating flow of the primarysubstrate with flow of the contaminated stream to be detoxified in acyclic fashion, improves economic viability over processes which allowsimultaneous presence of both the primary substrate and the targetcontaminants in the packing or other biodegradation media. However, inpractice, a substantial quantity of chloroethylenes or other amenablecontaminants sorb to the biodegradation media during flow of thecontaminated stream, and when the primary substrate stream is againreturned to the process to sustain the microorganisms and generateenzymes needed for target contaminant degradation, presence of theprimary substrate causes the residual and sorbed target contaminants todesorb from the biodegradation media and escape to the environment,resulting in a substantial loss of process efficiency and economics.Furthermore, practical contact times required for economical commercialoperation dictate the incomplete utilization (direct metabolism) of theprimary substrate during single-pass and/or open-loop process flow, andits co-mingling with the target contaminants when they are againreturned to the system results in competitive inhibition of targetcontaminant degradation, allowing the target contaminants to passthrough the process undegraded and further decreasing process efficiencyand increasing process cost.

[0034] We have unexpectedly found that, for cometabolic processes,practicing the processes of the present invention utilizing novelclosed-loop recycle operation schemes take advantage of theadsorption-desorption dynamics within the biodegradation media andunexpectedly (1) provide efficient and complete direct metabolism ofprimary substrates (food sources), whether they themselves be pollutantsor harmless compounds, without loss or venting of the primary substratesto the environment, (2) allow enzymatic degradation (cometabolism) ofsorbed or residual target contaminants during feeding of the primarysubstrates to the microorganisms without loss or venting of the primarysubstrates or target contaminants to the environment, (3) virtuallypreclude co-mingling of primary substrates with target contaminants andthereby achieve high target contaminant degradation efficiency, (4)utilize naturally occurring microorganisms widely available in theenvironment, and (5) self-optimize to maintain the optimal microbialtypes and populations without the need for microorganism replenishmentor modification, thus dramatically improving the simplicity, economics,and practicability of such processes.

[0035] Scientific wisdom indicates that said closed-loop recycle schemesshould deplete the oxygen supply in the closed system, resulting in lossof the aerobic microorganisms and failure of the process. However, thenovel closed-loop recycle schemes of the present invention unexpectedlyresult in dramatic improvements in process efficiency and economicswhile self-optimizing the microbial types and populations to the chosenprimary substrate(s) (in cometabolic processes) and the site-specifictarget pollutants and other environmental characteristics.

[0036] With use of the novel closed-loop recycle schemes of the presentinvention for cometabolic or direct metabolic processes, oxygen demandfor the primary substrate and/or pollutant should deplete the oxygensupply, kill the aerobic microorganisms, and render the process useless.Unexpectedly, oxygen levels are reduced only slightly, defyingconventional scientific wisdom concerning the function of the aerobicmicroorganisms. The closed loop recycle schemes dramatically reduce use(cost) of the primary substrate, eliminate target pollutant emissionsduring feeding of the microorganisms, and reduce overall pollutantemissions, which in turn dramatically improves process efficiency andreduces process capital and operating costs.

[0037] We have also unexpectedly found that, for pollutants capable ofbiodegradation via direct metabolism only, practicing the processes ofthe present invention utilizing novel closed-loop recycle operationschemes take advantage of the adsorption-desorption dynamics within theprocess and unexpectedly (1) provide efficient and complete directmetabolism of the contaminants without loss or venting of thecontaminants to the environment, (2) utilize naturally occurringmicroorganisms widely available in the environment, and (3)self-oppimize to maintain the optimal microbial types and populationswithout the need for microorganism replenishment or modification, thusdramatically improving the simplicity, economics, and practicability ofsuch processes.

[0038] It is therefore the principal object of the present invention toprovide novel, efficient, and economical ex situ processes utilizingclosed-loop recycle schemes for cometabolic enzymatic degradation ofchloroethylenes and other amenable contaminants which alone are noteasily or efficiently degraded by naturally occurring microorganisms andfor direct metabolic degradation of a wide variety of other amenablecontaminants.

[0039] Another object of the present invention is to provide saidcometabolic processes such that flow of the waste or contaminatedstreams is substantially separated from flow of the primary substratestreams into separate and discrete process cycles to minimize oreliminate co-mingling of the primary substrate with the targetcontaminants to avoid loss of contaminant degradation efficiency.

[0040] A further object of the present invention is to provide saidprocesses with microbially self-optimizing characteristics which forcethe adaptation, dominance, and maintenance of the microbial types andpopulations that provide optimal degradation of the target contaminants,without the need for addition or replenishment with pure, externallygrown strains of microorganisms, and rather, allowing no initialinoculation or the initial inoculation of the processes with the wastestream to be detoxified or with soil sediments or water collected fromwidespread environments which are contaminated with the targetcontaminants or other site-specific amenable contaminants targeted fordetoxification.

[0041] A still further object of the present invention is to providesaid cometabolic processes with novel closed-loop recycle schemes inwhich the processes are periodically closed the outside environment andthe enclosed process streams are recirculated within the process which(1) provide efficient and complete direct metabolism of primarysubstrates (food sources), whether they themselves be pollutants orharmless compounds, without loss or venting of the primary substrates tothe environment, (2) allow enzymatic degradation (cometabolism) ofsorbed or residual target contaminants during feeding of the primarysubstrates to the microorganisms without loss or venting of the primarysubstrates or target contaminants to the environment, (3) virtuallypreclude co-mingling of primary substrates with target contaminants andthereby achieve high target contaminant degradation efficiency, (4)utilize naturally occurring microorganisms widely available in theenvironment, and (5) self-optimize to maintain the optimal microbialtypes and populations without the need for microorganism replenishmentor modification, thus dramatically improving the simplicity, economics,and practicability of such processes.

[0042] A still further object of the present invention is to providesaid direct metabolic processes with novel closed-loop recycle schemesin which the processes are periodically closed the outside environmentand the enclosed process streams are recirculated within the processwhich (1) provide efficient and complete direct metabolism of thecontaminants without loss or venting of the contaminants to theenvironment, (2) utilize naturally occurring microorganisms widelyavailable in the environment, and (3) self-optimize to maintain theoptimal microbial types and populations without the need formicroorganism replenishment or modification, thus dramatically improvingthe simplicity, economics, and practicability of such processes.

[0043] Still further and more general objects and advantages of thepresent invention will appear from the more detailed description setforth below, it being understood, however, that this more detaileddescription is given by way of illustration and explanation only and notnecessarily by way of limitation, since various changes therein may bemade by those skilled in the art without departing from the true scopeand spirit of the instant invention.

DESCRIPTION OF THE DRAWINGS

[0044] The present invention, together with further objects andadvantages thereof, will be better understood from a consideration ofthe following description taken in connection with the accompanyingdrawings and examples in which:

[0045]FIG. 1 is a flow sheet generally illustrating the cometabolicand/or direct metabolic processes of the present invention.

[0046]FIG. 2 shows: Demonstration Unit Operation without Closed-LoopRecycle Feeding.

[0047]FIG. 3 shows: Effect of Delaying Start of Propane Feed in TVABench-Scale Biofilter.

[0048]FIG. 4 shows: Effect of Closed System Operation During Part ofFeeding Cycle.

[0049]FIG. 5 shows: Zero Effluent TCE and 100% Propane UtilizationDuring Closed-Loop Recycle.

[0050]FIG. 6 shows: Effect of Load on Degradation Rate in DemonstrationUnit.

[0051]FIG. 7 shows: Effect of Influent Load on Degradation Rate andEfficiency in Demonstration Unit with EBCT=30 Minutes.

[0052]FIG. 8 shows: Effect of Breakthrough on Effluent Concentration inDemonstration Unit.

[0053] FIGS. 2-8 pertain to the EXAMPLES, infra, where they arediscussed in detail.

[0054]FIG. 1 is a flow sheet generally illustrating the principles ofour new and novel processes for the simple, effective, and economicalcometabolic degradation of chloroethylenes and other amenable,site-specific target contaminants. Although the description and exampleswhich follow are conveniently directed to a continuous operation fordetoxifying a gaseous stream contaminated with TCE and dichloroethylene(DCE) and utilizing propane as the primary substrate, those skilled inthe art will readily appreciate that only simple modifications andadjustments are necessary to practice the processes of the instantinvention (1) on a continuous, recycle operation basis, (2) on a batchoperation basis, (3) on a batch, recycle operation basis, (3) fordetoxifying streams contaminated with other compounds amenable tocometabolic degradation through use of primary substrates, (4) fordetoxifying contaminated liquid streams, (5) with primary substratesother than propane, (6) for detoxifying streams contaminated with a widevariety of compounds capable of direct metabolism by naturally occurringmicroorganisms and not requiring a cometabolism step, and/or (7) usingvarious combinations of process variations (1) through (6).

[0055] As will easily be appreciated by one skilled in the art, a directmetabolism process in accordance with the present invention isessentially a cometabolism process in accordance with the presentinvention except that the target contaminant cometabolic degradationstep is omitted and only the direct metabolic metabolism step exists.

[0056] Referring now more specifically to FIG. 1 which illustrates oneexample process of the instant invention, the process operates in twoseparate and discrete cycles, the target contaminant cometabolicdegradation cycle and the primary substrate direct metabolism cycle,supra, one alternating with the other. The influent, effluent, andinternal process flows are controlled to specific values with respect toon or off mode, flow rate, concentration, and/or other pertinentparameters necessary to effect the required performance characteristicsof the process for the specific waste stream being decontaminated. Theseprocess parameters are automatically controlled by means of timers,controllers, control valves, control dampers, flammable gas sensors andcontrollers, and other various control equipment. For the present caseof decontaminating a gas-phase contaminated waste stream, electronicallycontrolled dampers and control valves automatically direct process flowsin the proper directions and at the proper rates when the appropriatetime has been reached to end one cycle and begin another cycle or whenthe appropriate time has been reached within a specific cycle to changepertinent process parameters such as primary substrate rate orclosed-loop recycle flow rate. Referring again to FIG. 1 for the exampleof open-loop, single-pass operation during the contaminant cometabolicdegradation cycle, supra, a contaminated air stream flows from a sourcenot shown through line 1, and on through damper 2, which for saidprocess cycle is set in the open position to allow flow. Thecontaminated air stream from damper 2 then flows through line 3 tobiofilter 5, (traditionally termed “bioreactor” for liquid-phasedecontamination applications) where the contaminated air stream passesthrough the biodegradation media, and the contaminants are degraded tonon-toxic compounds by way of enzymes produced by the microorganismsduring a prior primary substrate direct metabolism feeding cycle. Thebiodegradation media can consist of a wide variety of natural packings,such as composts, or synthetic packings, such as pall rings or activatedcarbon, with the microorganisms immobilized and growing in and on thesaid packing. In some cases, moisture is provided to the packing if thegaseous contaminated stream does not provide sufficient moisture for theviability of the microorganisms. The now-detoxified clean air exits thebiofilter through line 6 and passes on through damper 7, which is set inthe open position. The clean air does not flow into line 9 becausedamper 10 has been automatically set in the closed position. The cleanair from damper 7 then flows on through line 8 to exit the process tothe atmosphere.

[0057] Referring again to FIG. 1 for closed-loop recycle operationduring the primary substrate feeding cycle, damper 2 is automaticallyset in the closed position at the beginning of said cycle to stop flowof the influent contaminated air stream through line 3. The gas in line3 is fed by a blower or fan not shown through line 3 and on to biofilter5. At the appropriate time during the cycle and at the appropriate ratesand intervals, primary substrate, preferably propane in this exampleapplication, is fed through line 4 from a propane tank not shown withits rate controlled by an automatic control valve as well as timers toprovide intermittent flow. The primary substrate leaving line 4 entersline 3 and mixes with the recirculating air in line 3, supra, and theresulting air-primary substrate mixture continues on through line 3 andenters LEL sensor 12, which is connected to a control valve not shownwhich controls flow of the primary substrate absolutely precluding anyflammable gas mixtures from being produced and absolutely precluding anyflammable gas mixtures from existing anywhere in the process or outsidethe process. (Two other redundant control loop safeguards were used inthe example of the present invention which involved automatic cessationof propane flow when air rate fell below certain levels and automaticcessation of propane flow with failure of the air blower). Thenonflammable air-primary substrate mixture then continues to flowthrough line 3 and on to biofilter 5 where the primary substrate and airstream pass through the biodegradation media and the primary substrateis directly metabolized to provide growth of the microorganisms and thenecessary enzymes are produced for cometabolic degradation of the targetcontaminants. During passage of the air-primary substrate mixturethrough the biofilter, any residual target contaminants left in theinternal air of the now-closed process at the beginning of the cycle, aswell as any target contaminants adsorbed in the biodegradation mediaduring the contaminant cometabolic degradation cycle, in this exampleTCE and DCE, are also cometabolically degraded, albeit with lessefficiency than during the separate contaminant cometabolic degradationcycle, but without the release of the target contaminants from theprocess that would occur with single-pass open-loop operation during theprimary substrate feeding cycle. The internal process gas leavesbiofilter 5 through line 6 and enters line 9, the closed-loop recycleline, because damper 7 has automatically been set in the closed positionat the beginning of the primary substrate feeding cycle. The internalprocess gas continues through line 9 and on through damper 10 which isnow set in the open position. The internal process gas flows from damper10 through line 11 and then on through line 3 again. The internalprocess gas does not flow through line 1 because damper 2 is in theclosed position. The internal process gas is recirculated through line3, primary substrate enters line 3 through line 4, the internal processgas and primary substrate mix and flow on through LEL sensor 12 and onto biofilter 5 and this closed-loop recirculation flow is repeated untilthe prescribed time for the primary substrate direct metabolic feedingcycle to end and the next contaminant cometabolic degradation cycle tobegin, said prescribed time as well as other process parameters of theprimary substrate feeding cycle being preset and controlled to achievethe required process efficiency performance as a function of thecharacteristics of the specific waste streams being decontaminated.

[0058] For cometabolic detoxification of liquid streams, thecontaminated liquid is preferably trickled or sprayed down through thebiodegradation media in the bioreactor during the contaminantcometabolic degradation cycle. Clean air is passed through thebioreactor at rates only high enough to provide sufficient air tosustain the aerobic microorganism and allow cometabolic enzymaticdegradation of the target contaminants so as to minimize loss of targetcontaminants to the environment through vaporization of the contaminantsfrom the liquid stream into the air. Preferably, during the contaminantcometabolic degradation cycle with liquid-phase waste streams, thebioreactor air is recirculated in closed loop fashion, the bioreactor iscompletely closed to the outside environment to preclude any vaporrelease of the target contaminants, and the bioreactor is purged withfresh air for short duration only as often as is necessary to providesufficient oxygen to sustain the aerobic microorganisms and allowcometabolic enzymatic degradation of the contaminants to furtherminimize or eliminate target contaminant loss through vaporization fromthe liquid contaminated stream. During the contaminant cometabolicdegradation cycle, the process scheme for detoxification of liquidstreams can be operated in either a single-pass mode or with closed-looprecycling of the air, liquid, or both. With single pass operation ofboth the air and liquid, the air is preferably fed to the top of thebioreactor. Closed loop recycle operation of the air stream can beemployed during the contaminant cometabolic degradation cycle to improveprocess performance by controlling process parameters so as to meet gasand water emission discharge standards or regulations. Fordetoxification of liquid streams, closed-loop recycle operation duringthe primary substrate direct metabolic feeding cycle is the same as thatdescribed above for detoxification of gaseous streams.

[0059] For streams contaminated with compounds capable of directmetabolism by microorganisms, the cometabolic degradation cycle does notexist, and the processes of the instant invention consist of only adirect metabolic degradation cycle analogous to the said primarysubstrate direct metabolic degradation cycle, where the microorganismsprimary substrates, or food sources, become the contaminants targetedfor destruction by direct metabolism. For liquid-phase contaminatedstreams, the direct metabolic processes are operated using the novelclosed-loop recycle schemes of the instant invention such that theprocesses are closed to the outside environment and the bioreactor airis recirculated in closed loop fashion to preclude any vapor release ofthe target contaminants from the liquid. The bioreactor is only openedand purged with fresh air for short periods, preferably not untilcontaminants have been completely metabolized and preferably no moreoften than is necessary to replenish the aerobic microorganisms withsufficient oxygen to continue direct metabolism of the contaminantsthrough the next closed-loop recycle period. The liquid contaminatedstreams may be passed through the bioreactor on a continuous basis orcharged to the bioreactor on a batch basis and recirculated until thedesired degree of detoxification has occurred. For gaseous streamscontaminated with compounds capable of direct metabolism, the biofiltermay be charged on a batch basis with the gaseous stream to bedecontaminated and then closed and operated with closed-loop recycle topreclude escape of contaminants to the environment during directmetabolism until the desired degree of decontamination has beenachieved, at which time the biofilter is recharged with the contaminatedgas stream and the process repeated.

[0060] Of course, it will be appreciated that in still other embodimentsof the instant invention, there exist other variations to the processesof the instant invention illustrated by the example processes abovewhich will appear to those skilled in the art without departing from thetrue spirit and scope of the instant invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Terms Used Herein

[0061] In the following discussion, it should be understood that unlessotherwise clear from context the singular and plural are usedinterchangeably for brevity. For example, the process of the presentinvention can be used for the degradation of undesired organic chemicalsin general; however, often the singular undesired organic chemical willbe used.

[0062] Ex Situ Processes

[0063] “Ex situ” refers to outside of the contaminated environment asopposed to “in situ”, which refers to inside or within the contaminatedenvironment. In other words, an ex situ process refers to a separateand/or constructed process to which the contaminated stream is fed fromthe contaminated environment, whereas in situ methods refer to those inwhich the decontamination takes place within the contaminatedenvironment, e.g. within the contaminated soil or groundwater withouttheir prior removal.

[0064] Pollutant

[0065] In broad concept, a pollutant(s) in accordance with the presentinvention means any undesired compound which it is desired to degrade toa different desired form. The concepts of “undesired” and “desired” areof obvious flexibility, and are meant to include an essential change inthe starting organic compound (pollutant) to a different form withdifferent but preferred characteristics by the practice of the processesof the present invention.

[0066] It is our present view that the processes of the presentinvention will find most general use in the degradation of intractablecompounds which are viewed today as harmful to the environment to asubstance(s) which is accepted in context as harmless to theenvironment.

[0067] The pollutants which can be degraded by direct metabolism inaccordance with the present invention are not especially limited so longthey can be directly metabolized by the microorganisms as a sources offood and growth. In particular, a wide variety of volatile organiccompounds (VOCs) such as alcohols, ethers, esters, ketones, aromatics,and alkanes (e.g. fuels) fit into the category of compounds that arecapable of direct metabolism by naturally occurring microorganisms.

[0068] The pollutants which can be degraded by cometabolism inaccordance with the present invention are not especially limited so longas form a cometabolic degradation system with the primary substrate(s)and the microorganism(s). While a wide listing of such pollutants islater provided, of special interest are the chlorinated aliphatichydrocarbons, particularly such compounds which are unsaturated, such as1,1,2-tri-chloroethane, 1,1-dichloroethane, 1,2-dichloroethane,trichloroethylene, cis-1,2-di-chloroethylene,trans-1,2-dichloroethylene, 1,1-dichloroethylene, 1-2-dibromoethane, andvinyl chloride. Of particular interest in cometabolic processes istrichloroethylene.

[0069] The Microorganism(s)

[0070] The microorganism(s) useful in the present invention are aerobicmicroorganisms which, in the presence of a primary substrate (whichitself may be a pollutant), will produce an enzyme which will degradethe pollutant of interest. Aerobic, of course, means that oxygen must bepresent for the growth and reproduction of the microorganisms. In thisregard, the term aerobic as used herein is not intended to have anyother meaning than its conventional meaning. The oxygen needed tomaintain an aerobic environment can come from any source, for example,air, pure oxygen, a compound which can be degraded to produce oxygen,but as a practical matter the oxygen is typically passed to themicroorganisms in the system of the present invention in air. Wepresently see little, if anything, to be gained by using an oxygensource other than air due to increased costs.

[0071] The microorganisms useful in the practice of the presentinvention are preferentially naturally occurring aerobic microorganisms,as will now be discussed. These microorganisms are present everywhere inthe environment. In particular, microorganisms useful in practice of thepresent invention are present in the environment and/or waste streamthat is desired to be contaminated, so that there is no need for initialinoculation of the biofilters or bioreactors with isolated andconcentrated pure cultures, as the cultures which best thrive on thewaste streams fed to the biofilter or bioreactors will dominate, grow,and concentrate after feeding of the contaminated streams containing theadapted microorganisms is initiated.

[0072] However, though not necessary, there are certain methodsavailable known by those of ordinary skill in the art and taught in theprior art that are capable of concentrating and enriching microorganismsfrom a site targeted for decontamination such that the resulting desiredmicroorganism cultures are more dominant and such that, in certaincases, the time required for populating the biofilter or bioreactor withthe optimum strains of microorganisms can be reduced.

[0073] It will be appreciated by one of ordinary skill in the art thatthe techniques now to be described are well known and conventional inthe art for obtaining not only mixtures of microorganisms useful inaccordance with the present invention (often called microbial consortiaherein) but purified strains of such microorganisms isolated from soilor water.

[0074] One approach is to obtain a soil or water sample and enrich thesample for a mixture of microorganisms or isolate to form a purifiedculture of microorganisms with the ability to degrade one or morepollutants. One simple example procedure for obtaining a purifiedculture of microorganisms useful in accordance with the presentinvention comprises the steps of:

[0075] (1) collecting a sample of material from the site contaminatedwith obnoxious chemicals;

[0076] (2) enriching the microorganisms found living in the sample;

[0077] (3) separating the strains of microorganisms capable of havingdifferent metabolisms for the various chemicals in the sample from thesite, from each other;

[0078] (4) purifying the strains which are capable of biodegrading thechemicals to be disposed of;

[0079] (5) applying the strain to the locus of the contaminants to bedisposed of; and

[0080] (6) monitoring of removal of the contaminants in accordance withthe process of the present invention.

[0081] Finally, microorganisms capable of degrading target halogenatedaliphatic hydrocarbons or other compounds of interest can be selectedfrom mixed cultures by growing the culture in the presence of an inducer(primary substrate) capable of stimulating cometabolic biodegradation,under conditions such that the culture is enriched for microorganismscapable of degrading the target pollutant. Pure cultures of suchmicroorganisms can then be isolated by subculturing the enrichedpopulation using techniques well known to one of skill in the art.

[0082] More specifically, microorganisms can be isolated as follows.Soil samples are taken from the natural flora. A target halogenatedaliphatic hydrocarbon (or other compounds targeted for decontamination),in the presence or absence of an inducer (primary substrate), is addedto each sample. Microorganisms useful in the present invention may beisolated using many types of inducers, primary substrates, and/or targetpollutants. Each sample is then analyzed for pollutant degradationcompared to sterile controls. For each sample showing significant targetpollutant degradation, aliquots of the sample are plated onto agarplates. Colonies of the microorganisms are grown and each is tested forits ability to degrade the target pollutant in the present or absence ofan inducer.

[0083] A detailed procedure which can be used in accordance with thepresent invention with obvious modifications as disclosed in U.S. Pat.No. 4,925,802 Nelson et al. at col. 3, line 53 to col. 4, line 43 ishereby incorporated by reference.

[0084] A listing of primary substrates, microorganisms, and enzymes,where available, is later provided.

[0085] Biodegradation Media or Support

[0086] The microorganism(s) of the present invention can be immobilizedor supported on biodegradation media or packing, or they can berecirculated in the form of a nutrient-microorganism suspension spraythrough the process, as will be described in more detail in Example 7,infra. The packing type of the present invention is not important to thepractice of the present invention so long as the packing does notsignificantly harm the microorganism(s) or cometabolic enzymes andpermits adequate contact of the primary food sources and targetpollutants. Of course, the packing or support must retain themicroorganisms thereon and not itself be too rapidly degraded during theprocess of the present invention so that undesired early packing orsupport replacement is needed. So long as the above criteria are met,the substrate can be freely selected from natural or synthetic materialsor a mixture thereof. Examples are later given.

[0087] Biofilters/Bioreactors

[0088] The actual cometabolic or direct metabolic degradation ofpollutants to harmless byproducts with accordance of the presentinvention occurs in and on a supported living mass of microorganismswhich are in an aqueous environment, i.e., which are kept moist. By“aqueous environment”, we simply mean that sufficient water is presentwith the microorganisms to support their life and permit the pollutantsto contact the microorganisms and/or enzymes they produce where thepollutants will be degraded to harmless byproducts.

[0089] Where the pollutants are initially fed to the processes of thepresent invention in the form of a gas stream which passes over andthrough the supported bed of microorganisms, this system of the presentinvention is called a biofilter system.

[0090] Where the pollutants are initially fed to the processes of thepresent invention in the form of an aqueous stream carrying thepollutants which passes over and through the supported bed ofmicroorganisms, this system of the present invention is called abioreactor system.

[0091] In actuality, there is little difference between a biofiltersystem and a bioreactor system since in each instance the pollutants arecontacted with the microorganisms or the enzymes which degrade thepollutants to harmless byproducts, through and in the aqueousenvironment in which the microorganisms exist.

[0092] Batch, Continuous, Single-Pass, and Recycle

[0093] A batch process is one in which the process flows enter thereactor for a specific period of time and then stop, and the contents ofthe reactor are then allowed to act on the reactants in a mixed,recirculated, or non-mixed state until such time that the desiredchanges in the reactor contents are achieved, after which the contentsof the reactor are removed, and the reactor is then filled with anotherbatch of reactants and the process is repeated. A continuous process isone in which the process flows continuously enter and leave the reactorsuch that the desired change in the reactants is achieved as they passthrough and out of the reactor. Single-pass means that the reactantspass through the reactor one time, where as recycled means that part ofthe reactor effluents are fed back into the reactor or are fed back intothe reactor influent process streams. Combinations of batch andcontinuous mean that the process is operated on a batch basis part ofthe time and on a continuous basis part of the time. Combinations ofsingle-pass and recycled simply mean that the process flows are singlepass part of the time and recycled part of the time, either all or inpart, back to the reactor. Batch recycle simply means that the reactorcontents are moved out of the batch reactor and put back into the batchreactor with no net process flows entering or leaving the reactor, as isthe case with closed-loop recycle operation. With continuous operation,the are net flows entering and leaving the process.

[0094] Closed Loop Recycle/and Preventing Comingling of Process StreamsPertaining to Cometabolic Processes

[0095] The following pertains to the concepts of closed loop recycle andpreventing commingling (substantial) of process streams during suchclosed-loop recycle for pollutants requiring cometabolism. Hereinafterwe often refer to these concepts simply as closed-loop recycle andpreventing commingling of process streams. As will be clear from thefollowing discussion, however, the process streams are a primarysubstrate rich stream and a pollutant rich stream. Ignoring the sorptionof pollutant and primary substrate into the microorganism packing orsupport bed, which is later discussed in detail, a rather transientinterruption in the concept of not commingling process streams inaccordance with the present invention, due to the competition betweenthe primary substrate and the pollutant with respect to themicroorganisms, in an ideal process, the primary substrate rich streamand the pollutant rich stream would be separate, distinct streamswithout any primary substrate in the pollutant rich stream and,conversely, without any pollutant in the primary substrate rich stream.This ideal process is, however, impractical in practical commercialoperation where one is typically treating very large amounts of apollutant laden gas (biofilter) or a pollutant laden waste water stream(bioreactor). Thus, the practical realities of the process of thepresent invention with regard to cometabolic processes are now discussedwith reference to the balance and trade-offs involved.

[0096] The processes of the present invention for cometabolic processesinvolves two cycles, one where the primary substrate rich stream iscontacted with the support bed containing microorganisms (feed cycle)and one where the pollutant rich stream is contacted with the supportbed containing microorganisms for contact with the degrading enzymes viaa cometabolic pathway (degradation cycle).

[0097] The concept of closed-loop recycle in accordance with the presentinvention for cometabolic processes is intimately related to the conceptof preventing substantial commingling of the primary substrate richstream and the pollutant rich stream during the process of the presentinvention.

[0098] For pollutants requiring cometabolic degradation, the processesof the present invention always involve two substantially distinctprocess streams, one of which can be viewed as a primary substrate richstream and the other of which can be viewed as a pollutant rich stream.

[0099] The function of the primary substrate rich stream is to carry theprimary substrate to the mass of microorganisms on the packing used sothat the primary substrate can be consumed by direct metabolism as afood source by the microorganisms, to sustain life and reproduction ofthe microorganisms and induce the microorganisms to produce the enzymesneeded for the cometabolic degradation of the pollutant.

[0100] The function of the pollutant rich stream is to bring thepollutant into contact with the enzymes generated by the microorganismsfor the cometabolic degradation of the pollutant by the enzymes.

[0101] Either or both of the primary substrate rich stream or thepollutant rich stream can be contacted with the microorganisms on thepacking in the closed loop recycle mode. However, as will later beexplained in more detail, it is most preferred that at least the primarysubstrate rich stream be contacted with the microorganisms on thepacking in the closed loop recycle mode.

[0102] Thus, by closed loop recycle mode, we mean that either theprimary substrate rich stream, the pollutant rich stream (or both,albeit in different cycles) is contacted with the microorganisms on thepacking and repeatedly passed over and through the microorganisms on thepacking until the desired degree of nutrition and feeding and associatedgeneration of the target-pollutant-degrading enzymes is achieved (feedcycle) or repeatedly passed over the microorganisms on the packing untilthe desired degree of target-pollutant degradation is achieved(cometabolic degradation cycle).

[0103] In closed-loop recycle operation, the loop, which can be in theform of piping, ductwork, or other appropriate materials for transfer offluids, serves only as a means to transfer the interior contents of thebiofilter or bioreactor from one point to another within the closedsystem, for example, from the effluent port to the influent port, toenable the internal contents of the closed biofilter or bioreactor to berepeatedly recirculated or passed through the biofilter or bioreactorwhere the biodegradation is occurring. The loop, or conduit, tofacilitate closed-loop recycling or recirculation is not considered tobe an important part of the process with respect to biodegradationoccurring in the loop as compared with the biodegradation occurring inthe biofilter or bioreactor degradation media. Although it is possiblefor biodegradation to occur as the materials flow through the closedloop, or conduit, during recycle from one point in the biodegradationmedia to another, it is not considered to be a major point ofbiodegradation as it does not normally contain major concentrations ofthe microorganisms. One case in which some biodegradation would occur induring transfer through the loop would be in the case of usingclosed-loop recirculation of a nutrient-microorganism spray instead ofsupport or packing, as described supra, and as described in more detailin Example 7, infra.

[0104] However, this “closing” of the recirculating primary substraterich stream or pollutant rich stream does not absolutely preclude theaddition small quantities of materials so long as such addition does notadversely affect the desired function of these two cycles, primarilymicroorganisms nutrition/inducement of enzyme production for thesubsequent cometabolic pollutant degradation during the contact of thepollutant rich stream with the microorganisms on the packing. Thus, thespirit of the process of the present invention for cometabolic processesis not avoided by, for example, adding some incidental amount of primarysubstrate during the feed cycle, so long as the desired functions ofthese cycles can be achieved.

[0105] Obviously the concept of achieving the desired function of acycle is one of degree, and not subject to precise quantification. Asgeneral guidelines, however, clearly if the nature of a recirculatingprimary substrate rich stream were changed so as to affect the feedcycle to the point where the microorganisms on the packing were harmedor enzyme generation was insufficient to achieve the desired degree oftarget pollutant degradation, that would be a substantial impairment ofthat particular cycle.

[0106] Although the factors involved with respect to the nature of arecirculating pollutant rich stream are somewhat different, if thenature of such a recirculating stream were changed so that undesirableaffects resulted, for example, excessive competition between the primarysubstrate and the pollutant so that pollutant degradation was harmed,excessive time required for the desired degree of pollutant degradation,etc., quite obviously that would be a substantial impairment of thedegradation cycle.

[0107] The above discussion should make clear the concept of precludingsubstantial commingling of the primary substrate rich stream (feedcycle) and the pollutant rich stream (cometabolic degradation cycle) inaccordance with the present invention.

[0108] On a lab or bench scale, one could theorize a system where theprimary substrate is contacted with the microorganisms on the packinguntil all desired effects of the direct metabolism feed cycle areachieved in the complete absence of the target pollutant, the system ispurged with, e.g., pure oxygen under conditions controlled to ensuremaximum microorganism health and enzyme production, and thereafter thepollutant rich stream is introduced, whereafter the system is purgedwith, e.g., pure oxygen under similar controlled conditions areachieved.

[0109] However, on a practical commercial level such two completelydistinct, separate systems are not practical or feasible. Thus, on apractical commercial level there will always be some, albeit at timesvery low, amount of target pollutant in the primary substrate richstream and some primary substrate in the pollutant rich stream. This isbecause of the cycling of the primary substrate rich stream (feed cycle)followed by the cycling of the pollutant rich stream (cometabolicdegradation cycle).

[0110] Having thus discussed the general terms used in the presentinvention, we now turn to a more detailed explanation of the presentinvention for pollutants requiring cometabolism.

[0111] Cometabolism

[0112] To appreciate the present invention for pollutants requiringcometabolism for degradation, it is necessary to understand thecometabolism process which is used in the present invention.Cometabolism is a known process. In the context of the presentinvention, cometabolism involves:

[0113] at least one microorganism (typically a consortium or pluralityof microorganisms);

[0114] at least one target compound or contaminant (which for manyapplications of the present invention may be the only target compound orcontaminant of any practical interest); and

[0115] at least one primary substrate, which may be considered a foodsource for the at least one microorganism.

[0116] Oxygenases are enzymes that catalyze the incorporation of oxygen(O₂) into organic compounds. There are two kinds of oxygenases:dioxygenases catalyze the incorporation of both atoms of O₂ into themolecule and monooxygenases catalyze the transfer of only one of the twoO₂ atoms to an organic compound as a hydroxyl (OH) group, with a secondatom of O₂ ending up as water, H₂O. Because monooxygenases catalyze theformation of hydroxyl groups (OH) in organic compounds, they aresometimes called hydroxylases. Because monooxygenases require a secondelectron donor to reduce the second oxygen atom to water, they are alsosometimes called mixed-function oxygenases.

[0117] Various kinds of microorganisms, for example, Nocardia,Pseudomonas, Mycobaterium, and certain yeasts and molds, can utilizehydrocarbons for growth. Utilization of aliphatic hydrocarbons byaerobic microorganisms is strictly an aerobic process; in the absence ofO₂, hydrocarbons are unaffected by aerobic microbes. The initialoxidation step of aliphatic hydrocarbons involves molecular oxygen (O₂)as a reactant, and one of the atoms of the oxygen molecule isincorporated into the oxidized hydrocarbon. In the oxidation ofaliphatic hydrocarbons, monooxygenases are most generally involved, andthe initial oxidation need not be at a terminal carbon in all cases.

[0118] The breakdown of aromatic hydrocarbons involves the action ofeither oxygenases or mixed-function oxygenases.

[0119] It is known that organisms that are able to metabolizehalogenated compounds are fairly diverse, including genera of bothbacteria and fungi. Some halogenated compounds serve well as carbon andenergy sources and are oxidized completely to CO₂. However, othercompounds are much more recalcitrant, and are attacked only slightly ornot at all, although they may often be degraded provided some otherorganic material is present as a primary energy source, a phenomenoncalled cometabolism.

[0120] Thus, in the context of the present invention, cometabolism isthe microbial transformation of a compound, often called a targetcompound or contaminant, that cannot be used for growth or energy. As aconsequence, for the cometabolic process to occur there must be aprimary substrate (food) available that the microorganisms can use forenergy and growth. A resuht of the microorganisms utilizing the primarysubstrate is the production of an enzyme that will catalyze thetransformation or degradation of the undesired target compound orcontaminant in an aqueous environment to relatively harmless orrelatively innocuous end products. The transformation or degradation ofthe undesired contaminants occurs due to the non-specific nature of theenzyme(s) produced from the primary substrate(s). The cometabolicprocess is the principle degradation pathway for several highlyrecalcitrant compounds.

[0121] TCE, a target compound or contaminant of particular interest inaccordance with the present invention, can be degraded by methanotrophs,phenol degraders, propane oxidizers, ammonia oxidizers, toluenedegraders, and others as a result of their ability to produce thenonspecific enzymes necessary for the cometabolic process to occur. Theenzymes involved in TCE degradation by these organisms include methanemonooxygenase, toluene dioxygenase (TOD), toluene-2-monooxygenase (TON),toluene-3-monooxygenase (TBU), toluene-4-monooxygenase (TMO), propanemonooxygenase, and ammonia monooxygenase. These organisms only producethe cometabolic enzymes when exposed to specific growth substrates,usually easily identified from their name. For example, aphenol-degrading bacteria may be capable of using glucose as a growthsubstrate, but under this condition, it will not produce the oxygenaseenzymes which enable the cometabolic transformation of chlorinatedaliphatic compounds (CACs). Phenol must be present within the system tostimulate appropriate enzyme production

[0122] Hereinafter, the following abbreviations are used:CAC—chlorinated aliphatic compound; PAH—polyaromatic hydrocarbon (orpolynuclear aromatic hydrocarbon); PCB—polychlorinated biphenyl; andTCE—trichloroethylene.

[0123] It is contemplated that the processes of the present inventionwill find application with all of the following cometabolie-basedprocesses.

[0124] For example, Providenti, M. A., H. Lee & J. T. Trevors (1993)Selected factors limiting the microbial degradation of recalcitrantcompounds. Journal of Industrial Microbiology 12, 379-395, teach avariety of target compounds or contaminants can be degraded throughcometabolism, for example the aerobic degradation of PCB may require acometabolite such as biphenyl, 4-chlorobiphenyl, benzoate or2-chlorobiphenyl; the aerobic degradation of 1- and 2-chloronaphthalenesrequires naphthalene; the aerobic degradation of high molecular weightPAHs such as dibenzothiaphene, pyrene and fluoranthrene requires analternate carbon source such as glucose; the aerobic degradation of 1and 2 carbon atom chlorinated aliphatic compounds, e.g., TCE, has beenshown to occur with the cometabolic oxidation of methane, propane,formate, phenol, toluene, or ammonia.

[0125] A substantial amount of prior art teaches cometabolic systems forthe transformation or degradation of CACs including TCE as now discussedin detail.

[0126] Vanelli et al 1990, Degradation of Halogenated AliphaticCompounds by the Ammonia-Oxidizing Bacterium Nitrosomonas europaea.Appl. Environ. Microbiol. 56:1169-1171, dealing with CACs such asdichloromethane dibromoethane, chloroform, bromoethane,1,2-dibromoethane, 1,1,2-trichloroethane, 1,1,1-trichloroethane,1,2,3-trichloropropane, vinyl chloride and TCE, where the primarysubstrate is ammonia, the responsible organism is Nitrosomonas europaeaand the enzyme is ammonia monooxygenase.

[0127] CACs including TCE, Fox et al, 1990, where Methylosinustrichosporium OB3b utilizes methane as the primary substrate in acometabolic process. The enzyme methane monooxygenase is produced andCACs are degraded.

[0128] CACs, including TCE, where the primary substrate is methaneand/or propane, and the responsible organisms are a propane and methaneoxidizing consortium.

[0129] Chang Alvarez-Cohen, 1995. Model for the cometabolicbiodegradation of chlorinated organics. Environ. Sci. Technol. 29:2357-2367, where microorganisms produce non specific oxygenase enzymesthat can oxidize both their parent growth substrate and the cometabolicsubstrate. The oxidation of CACs, including TCE, generates short-livedintermediate products that damage cells and inactivate enzymes.

[0130] Ely et al, 1997, Cometabolism of Chlorinated Solvents byNitrifying Bacteria: Kinetics, Substrate Interactions, Toxicity Effects,and Bacterial Response. Biotechnology and Bioengineering vol. 54. No. 6,520-534; pure cultures of ammonia-oxidizing bacteria, Nitrosomonaseuropata, can cometabolize CAC's, including TCE, in the presence ofammonia. The non-specific enzyme produced is ammonia monooxygenase.

[0131] The following references are specific to the cometabolictransformation or degradation of TCE.

[0132] Wackett et al 1988. “Degradation of Trichloroethylene by TolueneDioxygenase in Whole-Cell Studies with Pseudomonas Putida F1.” Apl.Environ. Microbiol. 54(7): 1703-1708; TCE is degraded throughcometabolism. The organism Pseudomonas putida F1 is induced with tolueneto produce the nonspecific enzyme toluene dioxygenase capable of thedegradation of TCE.

[0133] Hopkins et al, 1993, where the primary substrate is phenol and amixed microbial consortium is used.

[0134] Folsom et al 1990, Performance of a Recirculating Bioreactor forthe Degradation of TCE. Bioremediation of Hazardous Wastes.EPA/600/9-90/041. U.S. Environmental Protection Agency, Office ofResearch and Development, Biosystems Technology Development Program,Washington, D.C. Pp. 6-8 (ERL,GB X726), where the primary substrate(s)is toluene, o-cresol, m-cresol or phenol and Pseudomonas cepacia strainG4 is used.

[0135] Alexander's Gas and Oil Connection Reports. “Bioremediation ofhydrocarbon pollutants with butane-utilizing bacteria.” Volume 4, issue#9—Tuesday, May 11, 1999, where the primary substrate is butane andbutane-utilizing bacteria are used, suitable butane-utilizing bacteriainclude suitable Pseudomonas, Variovorax, Nocardia, Chryseobacterium,Comamonas, Acidovorax, Rhodococcus, Aureobacterium, Micrococcus,Aeromonas, Stenotrophomonas, Sphingobacterium, Shewanella,Phyllobacterium, Clavibacter, Alcaligenes, Gordona, Corynebacterium andCytophaga.

[0136] Wilson, J. T. and B. H. Wilson. 1985 Biotransformation oftrichlorethylene in soil. Appl. Env. Microbiol. 49, 242-243, where theprimary substrate is methane and a mixed methantrophic microbialconsortium is used, specifically a soil column taken from a CACcontaminated site containing a natural population of microorganisms thatwould degrade TCE when stimulated with methane. This is the firstreference that noted aerobic TCE degradation.

[0137] Arciero, D., T. Vanelli, M. Logan, and A. B. Hooper, 1989.Degradation of trichloroethylene by the ammonia-oxidizing bacteriumNitrosomonas europaea. Biochem. Biophys. Res. Commun. 159, 640-643,disclosing the use of Nitrosomonas europaea, an ammonia-oxidizingbacteria, to degrade TCE through cometabolism. The primary substrate forthis system is ammonia. The non-specific enzyme produced through ammoniainduction is ammonia monooxygenase.

[0138] Brucceau, G. B., H. C. Tsien, R. S. Hanson, L. P. Wackett. 1990.Optimization of trichloroethylene oxidation by methanotrops and the useof colorimetric assay to detect soluble methane monooxygenase activity.Biodegradation. 1: 19-29, where TCE is degraded by methanotrops througha cometabolic process that utilizes the enzyme methane monooxygenase.

[0139] Hopkins, G. D., J. Munakata, L. Semprini, and P. L. McCarty.1993. Trichloroethylene concentration effects on pilot field-scalein-situ groundwater bioremediation by phenol-oxidizing microorganism.Environ. Sci. Technol. 27: 2542-2547, where phenol is used as theprimary substrate for a mixed microbial consortium.

[0140] Little, C. D., A. V. Palumbo, S. E. Herbes, M. E. Lidstrom, R. L.Tyndall, and P. J. Gilmer. 1988. Trichloroethylene biodegradation by amethane-oxidizing bacterium. Appl. Environ. Microbiol. 54: 951-956,disclosing the use of methanotrops where methane is the primarysubstrate to induce the production of the monooxygenase enzyme.

[0141] Oldenhuis, R. R., J. M. Vink, D. B. Janssen, and B. Witholt.1989. Degradation of chlorinated aliphatic hydrocarbons by Methylosinustrichosporium OB3b expressing soluble methane monooxygenase. Appl.Environ. Microbiol. 55, 2819-2826, where Methylosinus trichosporius OB3bused methane to generate the nonspecific soluble enzyme methanemonooxygenase to degrade TCE through a cometabolic process. Tsien, H.G., G. A. Brusseau, R. S. Hanson, and L. P. Wackett 1989. Biodegradationof trichloroethylene by Methylosinus trichosporium OB3b. Appl. Environ.Microbiol. 55:3155-3161, where Methylosinus trichosporius OB3b usedmethane to generate the nonspecific soluble enzyme methane monooxygenaseto degrade TCE through a cometabolic process.

[0142] Phelps et al, 1991, disclosing the use of a consortium oforganisms capable of utilizing methane and/or propane to producenonspecific enzymes that are capable of degrading TCE and other CACs.

[0143] Wackett, J. J., J. W. Mello, and R. F. 1984. The groundwatersupply survey. J. Am. Water Works Assoc. 5,52-59, disclosing the use ofpropane oxidizing organisms which are induced to produce a nonspecificoxygenase enzyme that is capable of degrading TCE.

[0144] The process of the present invention is not, of course, limitedto the above compounds. It is expected that the process of the presentinvention will be operable with the following cometabolic systems astaught in the following references.

[0145] Brunner, W., F. H. Sutherland, and D. D. Focht. 1985. “EnchancedBiodegradation of Polychlorinated Biphenyls in Soil by Analog Enrichmentand Bacterial Inoculation” J. Environ. Qual., Vol. 14, 324-328, wherethe target compounds are PCBs, the primary substrate is biphenyl, andAcinetobacter is used.

[0146] Mahaffey, W. R., D. T. Gibson, and C. E. Cerniglia. 1988.“Bacterial Oxidation of Chemical Carcinogens: Formation of PolycyclicAromatic Acids from Benz[a]anthracene.” Appl. Environ. Microbiol.54(10), 2415-2423., where the target compound is PAH benzo[a]anthracene,the primary substrates are m-xylene, biphenyl and salicylate, andwherein Beijerinckia Strain B-1 is used.

[0147] Mueller, J. G., P. J. Chapman, B. O. Blattmann, and P. H.Pritchard. 1990. “Isolation and Characterization of aFluoranthene-Utilizing Strain of Pseudomonas paucimobilis.” Appl.Environ. Microbiol., 56(4), 1079-1086, wherein the target compound is aPAH (pyrene 1,2-benzanthracene 3,4-benzpyrene 1,2,5,6-dibenzanthracene),the primary substrate is naphthalene, phenol or naphthalene andPseudomonas paucimobilis is used.

[0148] The above publications, from Providenti through Mueller, arehereby incorporated by reference with regard to their teachings onmicroorganisms and primary substrates.

[0149] In carrying out the objects of our present invention, novel,efficient, and economical ex situ processes utilizing closed-looprecycle schemes have been developed for ometabolic degradation ofchloroethylenes and other contaminants which alone are not easily orefficiently degraded by naturally occurring microorganisms and fordirect metabolism of a wide variety of other pollutants or otherundesirable compounds. The processes of the present invention are notlimited to utilization of any particular type of microorganism andpreferably utilize naturally occurring microorganisms which are widelyavailable in the environment, are easily obtainable from sources such assoil sediments and groundwater, are available in the waste streams to bedecontaminated, and are widely taught in the prior art, supra. Examplesof such naturally occurring microorganisms which may be utilized in theprocesses of the present invention include those discussed in the priorart previously incorporated by reference (U.S. Pat. No. 4,713,343,Wilson and Wilson, 1985; Wilson and Wilson, 1985; Fliermans et al. 1988;Wackett et al. 1989; Arciero et al. 1989; Hopkins et al. 1993; Nelson etal. 1987; Brusseau et al. 1990; Fox et al. 1990; Little et al. 1988;Oldenhuis et al. 1989; Tsien et al. 1989; Fennell et al.1993; Strandberget al. 1989; Tschantz et al. 1995; Alvarez-Cohen and McCarty, 1991;Semprini et al. 1990; Semprini et al. 1991; Chang and Alvarez-Cohen,1995; Phelps et al., 1991; Lackey, et al. 1993; Lackey et al. 1994).

[0150] The cometabolic processes of the present invention utilizeprimary substrates to induce enzymatic degradation of target pollutantssuch as chloroethylenes, particularly TCE, or other contaminantsamenable to such enzymatic degradation but which alone are not easily orefficiently biodegraded by such naturally occurring microorganisms.Further, the cometabolic processes of the present invention are operatedin a cyclical fashion such that feeding of the waste or contaminatedstreams is separated from feeding of the primary substrate streams intoseparate and discrete process cycles to minimize or eliminateco-mingling of the primary substrate with the target contaminants, whichis known to inhibit degradation of the target contaminants throughcompetitive inhibition by the primary substrate. Most importantly, theprocesses of the present invention utilize novel closed-loop recycleschemes which dramatically improve the efficiency, economics, andpracticability of degrading chloroethylenes, particularly TCE, and othersuch amenable contaminants requiring cometabolism. During theclosed-loop recycle periods, the processes are completely closed to theoutside environment with little or no net process flows entering orleaving the process. Scientific wisdom dictates that the oxygen demandduring closed-loop recycle should deplete the oxygen supply, resultingin loss of the aerobic microorganisms and failure of the process.Unexpectedly, oxygen levels are reduced only slightly, defyingconventional scientific wisdom concerning the function of the aerobicmicroorganisms, and dramatic improvements in process efficiency andeconomics are achieved.

[0151] The novel closed-loop recycle schemes of the present inventionfor cometabolic processes take advantage of the adsorption-desorptiondynamics within the biodegradation media and (1) provide efficient andcomplete direct metabolism of primary substrates (food sources), whetherthey themselves be pollutants or harmless compounds, without loss orventing to the primary substrates to the environment, (2) allowenzymatic degradation (cometabolism) of sorbed or residual targetcontaminants during feeding of the primary substrates to themicroorganisms without loss or venting of the primary substrates ortarget contaminants to the environment, (3) virtually precludeco-mingling of primary substrates with target contaminants and therebyachieve high target contaminant degradation efficiency, (4) utilizenaturally occurring microorganisms widely available in the environment,and (5) self-optimize to maintain the optimal microbial types andpopulations without the need for microorganism replenishment ormodification, thus dramatically improving the simplicity, economics, andpracticability of such processes.

[0152] The novel closed-loop recycle schemes of the present inventionfor direct metabolic degradation processes (consumption of the targetpollutants) also take advantage of the adsorption-desorption swingswithin the biodegradation media and (1) provide efficient and completedirect metabolism of the contaminants without loss or venting of thecontaminants to the environment, (2) utilize naturally occurringmicroorganisms widely available in the environment, and (3)self-optimize to maintain the optimal microbial types and populationswithout the need for microorganism replenishment or modification, thusdramatically improving the simplicity, economics, and practicability ofsuch processes.

[0153] The novel closed loop recycle schemes of the present inventionmay be used for treating either gas- or liquid-phase streams containingcontaminants capable of direct metabolism and/or contaminants requiringcometabolism. The processes may be applied on a batch or continuousbasis to contaminated soil and groundwater, to contaminated effluentsfrom a wide variety industrial operations such as solvent degreasing, orto wherever chloroethylenes or other such amenable contaminants exist.

[0154] The processes of the present invention are microbiallyself-optimizing in that the process schemes and parameters of thepresent invention bring about the adaptation, dominance, and maintenanceof the microbial types and populations within the biodegradation mediafor optimal degradation of the target contaminants, without the need forreplenishing the processes with pure, externally grown microbial strainsand without the need for the initial inoculation of the processes withspecially cultured, externally grown strains of microorganisms. Apreferred embodiment of present invention for pollutants requiringcometabolic degradation is the use of automatic, cyclically operated, exsitu biofilter or bioreactor processes in which feeding of the waste orcontaminated streams is separated from feeding of the primary substratestreams into separate and discrete process cycles to minimize oreliminate co-mingling of the primary substrate with the targetcontaminants. Thus, the primary substrate streams are fed to the processpart of the time to feed the microorganisms and activate the enzymesnecessary for contaminant degradation, and the contaminated streams arefed to the process part of the time to effect degradation of thecontaminants as they pass through the process. Continuous operation ofthe process can be provided by operation of dual biofilters orbioreactors so that one is being fed the waste streams while the otheris being fed the primary substrate streams. The waste streams andprimary substrate streams are then automatically switched to thealternate bioreactorsfbiofilters in cyclical fashion to allow continuousfeeding of the contaminated streams and primary substrate streams.However, the processes may be operated on a batch basis or in anintermittent fashion as well. In addition, the process may be operatedin a single pass mode or with recycle of the primary substrate andcontaminated streams. To allow use of only one bioreactor/biofilter inthe process, the incoming waste streams are stored as surge in a surgevessel for a period of time while the single bioreactor/biofilter isbeing fed the primary substrate stream to feed the microorganisms andactivate enzymes needed for contaminant degradation. After a period oftime, the primary substrate stream to the single bioreactor/bioreactoris discontinued, and the single bioreactor is then fed the stored wastestream to deplete the stored surge as well as the waste stream enteringthe surge vessel. The waste stream is detoxified by biodegradation as itpasses through the bioreactor/biofilter containing the necessaryenzymes. Of course, if flow of the contaminated streams are required tobe continuous to the process, the surge vessel is required to be of suchsize so as to accommodate the quantity of stored waste stream dictatedby the continuous flow rate of the waste stream and the period of timefor which the waste stream is to be stored.

[0155] The respective periods of time allowed each for flow of theprimary substrate streams and flow of the contaminated streams and theperiods of time allowed for each cycle of the process must be controlledto specific values to achieve the required performance characteristicsfor the process for the decontamination of a given site- andapplication-specific waste stream. The period of time allowed for eachcycle of the process is not necessarily equal to the period of timeallowed each for flow of the primary substrate streams or contaminatedstreams. Control and manipulation of these process variablesdramatically affect process efficiency and economic viability andspecific values for these process parameters are dependent on thecharacteristics of the waste and primary substrate streams, theperformance characteristics required of the process, and other importantconsiderations.

[0156] The most preferred embodiment of the present invention forpollutants requiring cometabolic degradation involves use of closed-looprecycle during the feeding cycle when the process is not receiving thetarget contaminant stream, although closed-loop recycle can also bebeneficially employed during at least part of the target contaminantdegradation cycle, particularly in applications involving detoxificationof liquid streams as previously described in DESCRIPTION OF THEDRAWINGS, supra. Practice of the processes of the present invention forcometabolic processes without use of the closed-loop recycle schemesresults in drastic loss of process performance and economics. Aprincipal advantage of the closed-loop recycle schemes involves savingsin operating cost by dramatic reduction in the quantity of primarysubstrate required, because all of the primary substrate is consumedwithin the process. However, other important advantages of theclosed-loop recycle schemes follow and are explained more fully in theEXAMPLES, infra, for the case involving TCE as the contaminant in a gasstream and propane as the primary substrate. During the closed-looprecycle feeding period, TCE adsorbed in the biofilter packing during theprevious target contaminant cometabolic degradation cycle is alsoenzymatically degraded with none released to the environment, so thatwhen TCE is again introduced to the biofilter after the closed-looprecycle period, the level of adsorbed TCE in the packing is lower; thus,the packing has more capacity to remove TCE through a combination ofadsorption and cometabolic degradation. Without the closed-loop recyclescheme, the TCE adsorbed in the packing and not yet destroyed bymicroorganisms during the contaminant degradation cycle is desorbed fromthe packing and released to the environment when the direct metabolismfeeding cycle again begins. Without closed-loop recycle during primarysubstrate feeding (single-pass feeding mode), effluent TCEconcentrations are higher during the propane feeding cycle (when theprocess is not receiving TCE) than during the TCE cycle (when theprocess is receiving TCE). Thus, the apparent TCE removal rate duringthe TCE cycle appears to be very high, but when the TCE released to theenvironment during the feed cycle is included in the overall materialbalance on influent and effluent TCE for the system, the realized TCEdegradation efficiency (and rate) is much lower, as will become apparentin the following examples.

EXAMPLES

[0157] In order that those skilled in the art may better understand howthe present invention may be practiced for simple, effective, andeconomical ex situ biodegradation of chloroethylenes, particularly TCE,and other such amenable contaminants targeted for detoxification, thefollowing examples are given by way of illustration only and notnecessarily by way of limitation. The experimental results herein wereobtained with a mobile Biofiltration Process Demonstration Unit, hereinafter referred to as the “Demonstration Unit”, mounted on a tractortrailer bed and installed in an area adjacent to groundwater airstripping and carbon filtration units at a site with TCE-contaminatedgroundwater.

Example 1

[0158] The Demonstration Unit consisted of an air stripper section and abiofilter section. The demonstration stripper was included only to allowvariation in the TCE concentration and rate of the air fed to thebiofilter. Contaminated groundwater from six wells is pumped to acollection sump and subsequently pumped to the air strippers, whichdischarge TCE-contaminated air to the atmosphere. This collection sumpwas the source of contaminated water for the stripper on theDemonstration Unit. Depending on the operating conditions chosen, partor all of the groundwater flowing into the collection sump was pumped tothe demonstration stripper where TCE and other volatile organiccompounds (VOCs) were stripped from the groundwater and transferred tothe stripper's effluent air stream. The air and water rate to thestripper were manipulated to control the rate and TCE concentration ofthe contaminated air fed to the biofilter. The contaminated air from thestripper was fed to the inlet of the biofilter and passed through thebiofilter to allow the microorganisms to destroy TCE and otherchlorinated organic compounds, and the treated air was released to theatmosphere.

[0159] The demonstration stripper consisted of a 32-inch diameter,9-foot high, 304 stainless steel tower packed with pall rings designedto maximize liquid-to-air contact. To operate the demonstrationstripper, contaminated groundwater was pumped from the collection sumpto the top of the stripper and allowed to flow down through the packingwhile fresh air flowed up through the bottom of the stripper. Volatileorganic compounds in the groundwater were transferred, or stripped, fromthe groundwater stream to the air stream. The treated water leaving thedemonstration stripper collected in a sump at the bottom of the stripperand was then pumped to the site's stripper for further processing. Airentering the demonstration stripper was drawn into the bottom of thevessel by a blower mounted on the discharge end of the demonstrationstripper.

[0160] During the demonstration, the inlet air and water flow rates tothe demonstration stripper were manipulated to control both the TCEconcentration and the TCE flow rate entering the biofilter. The air flowrate was set by a programmable controller. The water flow rate throughthe demonstration stripper was controlled by an automatic control valveand control loop using an inline magnetic flow meter and flowcontroller.

[0161] The TCE-contaminated air leaving the demonstration stripperpassed through the blower, flowed through the biofilter, and wasdischarged into the atmosphere.

[0162] The biofilter section of the Demonstration Unit consisted of arectangular vessel packed with a mixture of composted poultry litter andpine bark to support the microorganisms, as shown in the Table below.Composition of Biofilter Packing Material Material Weight % poultrylitter/pine bark compost 57 water 36 dolomitic limestone 5 chopped kenaf2

[0163] After installation of the biofilter system, the biofilter packingwas inoculated with a naturally occurring heterotrophic microbialconsortium obtained from several sites. This inoculum included bothmethane and propane-oxidizing consortiums obtained from Ada, Okla., amethanotroph from a waste disposal site near Oak Ridge, Tenn., and aTCE-degrading consortium from the Savannah River Plant, Aiken, S.C. Thisheterotrophic microbial consortium was capable of degrading TCE and manyother chlorinated aliphatic and aromatic compounds (Lackey, et al.1994). After being introduced to the biofilter, the microorganisms wereallowed to grow and acclimate by passing air and propane through thebiofilter for about a month prior to starting flow of the contaminatedair.

[0164] With respect to the microbial cultures used in our DemonstrationUnit, they were originally derived from sediments containing naturallyoccurring microorganisms collected in the field and grown as describedin Lackey, et al. 1994. Feasibility testing for the on-sitebioremediation of organic wastes by native microbial consortia.International Biodeterioration & Biodegradation. 33:41-59., the completetext (pp. 41-59) of which is hereby incorporated by reference. Themicrobial consortium is identified on page 43 as follows:

[0165] “Selection of Microbial Consortia

[0166] The consortium used for both test tube and bioreactor studiescontained mixtures of propane and methane-oxidizing bacteria obtainedfrom the vicinity of Ada, Okla. (Wilson & Wilson, 1985), a TCE-degradingconsortium isolated from the Savannah River Plant, Aiken, S.C.(Fliermans et al., 1988; Phelps et al., 1989) plus a methanotrophisolated from a waste disposal site near Oak Ridge, Tenn. The consortiumwas maintained on a phosphate and bicarbonate buffered mineral saltsmedium (Fliermans et al., 1988) supplemented with 5% methane and 3%propane (v/v, headspace).”

[0167] Samples of the microbial consortium cited, supra, (Lackey, et al.1994) were cultured to increase their population in the presence of air,propane, and TCE and then added to the compost packing of a bench-scalebiofilter which was fed only air, propane, and TCE; the developmentsmade in this biofilter led to the demonstration of the process asdescribed herein. Propanotrophic, TCE-degrading microorganisms from thepacking of this bench-scale biofilter, which had adapted andself-optimized the microbial types and populations to those whichprovided the optimum process performance, were used to inoculate thelarger biofilter of the Demonstration Unit as described herein. Althoughthe microbial consortium in the Demonstration Unit is likely differentin makeup than that described in Lackey, et al., 1994, due to differingprocess parameters, we firmly believe that one can use the fieldcollected source sediments as an inoculum for the processes of thepresent invention, feed the process propane and TCE exclusively, and theprocess will self-optimize the microbial consortium, adapting anddeveloping within the biodegradation media the optimum microbialconsortiums to achieve optimal process performance and economics, sincethe said source sediments were the initial starting materials from whichthe microbial consortium in the Demonstration Unit was derived. The sameis firmly believed to hold true for utilizing source sediments fromsites contaminated with other amenable contaminants as the microbialstarting materials for practicing the present invention for suchenzymatic degradation of said other amenable contaminants throughprimary substrate inducers.

[0168] Indeed, we further believe that the biodegradation media withinthe processes of the present invention can be inoculated with the sitewaste stream to be treated or with soil sediments or water collectedfrom widespread environments that are contaminated with TCE or otheramenable contaminants targeted for detoxification and that containdiverse, wild-type indigenous microorganisms which have adapted topresence of TCE or other such amenable contaminants in soil orgroundwater, as is amply described in prior art, or they may not beinoculated at all. There is no need to grow, isolate, and usespecialized microbial cultures or strains. The present invention's novelclosed-loop recycle schemes with repeated cyclical and alternatingfeeding of the primary substrate streams and contaminant streams havethe effect of forcing the adaptation, growth, and dominance of theoptimum microbial types and populations within the biodegradation mediato effect the most efficient and economical degradation of the targetcontaminants. In other words, the processes of the present invention areself-optimizing with respect to microbial types and populations.

[0169] The biofilter consisted of an approximately 8-foot wide, 16-footlong, and 9-foot high, rectangular, 304 stainless-steel vessel. Thebiofilter was initially packed with a mixture of composted poultrylitter, chopped kenaf (a bulking agent), and pelletized dolomiticlimestone (a buffering agent) to a depth of approximately 6 feet. Thepacking rested on a stainless steel wire-mesh floor and 1.5 feet of voidspace was provided just above and below the packing. During the processof transporting the Demonstration Unit, the packing settled to a depthof approximately 5 feet, leaving approximately 2.5 feet of void spaceabove the packing.

[0170] The Demonstration Unit was operated in two cycles: a TCEdegradation cycle and a propane feeding cycle. During the TCEdegradation cycle, contaminated water was pumped through thedemonstration stripper while fresh air was drawn through thedemonstration stripper and discharged into the biofilter.

[0171] The amount of time the system spent in each cycle was initiallyregulated with a series of timers. Later in the demonstration, theprocess was improved by the addition of a single multifunctionalcontroller which took over the functions of the multiple timers andprovided additional flexibility in operation, such as automaticallychanging the air flow rate during the TCE degradation and propanefeeding cycles.

[0172] During the propane feeding cycle, the flow of water to thestripper was discontinued and a stream of propane was fed into thebiofilter. Two feeding cycle operating modes were tested during thedemonstration: a single pass mode and closed-loop recycle mode. Whentesting the single pass mode, a controlled amount of propane wasinjected into the biofilter influent air stream. The air/propane mixtureflowed through the biofilter, where a portion of the propane wasconsumed, and the mixture was then discharged to the atmosphere via a3-foot tall stack on top of the biofilter. When testing the closed-looprecycle feeding mode, the biofilter was isolated from the stripper andatmosphere using a series of electronically controlled dampers. Oncethese dampers were properly positioned, the process was closed to theoutside environment and the internal air within the biofiltration systemwas continuously recycled on a closed-loop basis. A small amount ofpropane was fed into the closed biofiltration system during at least aportion of the closed-loop recycle mode of operation to feed themicroorganisms and activate the necessary enzymes for contaminantdegradation.

[0173] The propane was fed from a commercial 500-gallon tank through½-inch copper tubing. The rate of propane flow into the air stream wascontrolled with a mass flow controller equipped with control valve. Alower explosion limit (LEL) sensor located inside the influent airductwork and an associated control loop connected to a solenoid valve onthe propane feed line ensured that only non-flammable propane-airmixtures entered the biofilter. Additional safeguards were provided byinstalling control loops between the propane feed shut-off solenoidvalve and the air velocity sensor and air blower controller so thatpropane feed would automatically shut off if the air blower failed or ifthe air rate fell to a specified level. Additionally, the pressureregulator on the propane tank was set so that the maximum flow throughthe propane automatic control valve open at 100% would only slightlyexceed the set point of the propane flow controller.

[0174] With implementation of closed-loop recycle feeding, it becamenecessary to develop a different propane-addition scheme than was usedduring the simple, continuous one-pass flow used without recycle. Afeeding scheme was needed that would allow the closed system to becharged with as much propane (up to safe levels) in as short a period aspossible to maximize consumption and also allow time for completedepletion of the propane from the packing before reintroduction of TCE.To accomplish this with the simplified recycle system implemented,propane addition was carried out stepwise with timers which providedintermittent flow of propane in a repeated on-off fashion (e.g., 1minute on, 1 minute off, and so on) to ramp the concentration up untilthe propane in the closed system reached sufficiently high but safeconcentrations at which time the propane feed was discontinued and theair allowed to recirculate in the closed system for the remainder of thecycle to complete consumption of the propane. Propane addition maycommence at the very beginning of the closed-loop recycle phase ordelayed to a chosen point within the recycle phase depending on otheroperating conditions and chosen or dictated performance/costrequirements.

[0175] Throughout the demonstration, the biofilter packing was keptmoist by periodically pumping small amounts of water through a weepingtype hose arranged over the surface of the packing. During mostoperating periods, the high humidity of the stripper effluent air wassufficient to maintain the proper moisture levels. However, if moistureaddition became necessary (e.g., during hot weather periods with highair rates and short periods of stripper operation), then water wasobtained from the site's purified water source. Moisture addition wascontrolled to minimize or preclude drainage into the void area at thebottom of the biofilter.

[0176] The object of this field demonstration was to evaluate theefficacy of this biofilter process for destroying TCE and otherchlorinated compounds in contaminated air streams emitted fromoperations such as groundwater air stripping and solvent degreasing andto obtain information for scale up to commercial applications. Thisinvolved determining the effects of process variables on biofilterperformance parameters such as contaminant removal efficiency,contaminate removal rate, and operation costs. On-line, real-timeprocess monitoring was conducted by use of a gas chromatograph (GC),data loggers, a computer, and associated equipment located adjacent tothe biofilter in a portable trailer. The GC was equipped with anelectron capture detector (ECD), a flame ionization detector (FID), acolumn splitter, and a 10-way Valco valve to allow simultaneous analysisof both chlorinated aliphatic compounds and propane. Vacuum pumps andautomated valves provided continuous flows of influent and effluentprocess gases to the GC which automatically sampled the processes gasesevery 30 or 60 minutes and in some cases every 4 minutes (e.g., whencalibrating the GC and process equipment or when setting process feedrates). Data loggers collected and stored process data such as air flowrates, water flow rates, propane flow rates, propane concentrations (%of LEL), ambient and process stream temperatures, and oxygenconcentrations. The GC and data loggers were coupled to a computer whichwas connected via modem to a computer at TVA in Muscle Shoals, Ala.Remote operation software was used to provide remote real timemonitoring, downloading of process data, and control of some data loggerand GC functions.

[0177] This description of this field demonstration example is given byway of illustration only and is not intended to limit the scope of theinvention. Certain modifications and variations to the concept describedby this specific example will occur to those skilled in the art whichare within the true scope and spirit of the invention.

Example 2

[0178] Several parameters of the process of the present invention ingeneral as well as some parameters unique to the closed-loop recyclefeeding period significantly affect the operation, efficacy, economics,and performance of this biofilter process. The operating parameters andtheir approximate corresponding ranges as practiced in the Demonstrationof Example 1, supra, are shown in Table 1 and refer to a cometabolismprocess. However, these ranges are given by way of illustration only andare not intended to limit or restrict the scope of the present inventionso as to exclude operating ranges outside the ranges in theDemonstration of Example I or outside the ranges for direct metabolismprocesses. Explanation of process operating parameters in Table 1follows.

[0179] Closed-loop recycle refers to the mode of operation used duringthe feeding cycle when the process was not receiving the contaminatedair stream. “Yes” indicates that the process was operated in theclosed-loop recycle mode and “no” indicates that the process wasoperated in a single-pass mode with no recycle.

[0180] Influent TCE load is the mass rate of TCE in the biofilterinfluent air in grams of TCE per day per cubic meter of packing volume.

[0181] Influent TCE concentration is the TCE concentration in theinfluent air fed to the biofilter in parts per million by volume (ppmv).

[0182] Propane feed rate is the rate of propane flow rate to fed to thebiofilter.

[0183] Propane feed on interval is the period of time that the propaneflow was intermittently in the “on” position such that propane wasflowing to the process during the intermittent propane flow period inwhich the propane concentration within the internal process gas wasramped up during closed-loop recycle.

[0184] Propane feed off interval is the period of time that the propaneflow was intermittently in the “off” position such that propane was notflowing to the process during the intermittent propane flow period inwhich the propane concentration within the internal process gas wasramped up during closed-loop recycle. TABLE 1 Process Parameters andOperating Ranges During Demonstration of Example I Closed-loop(closed-system) recycle, yes or no yes or no Influent TCE load, g/day/m³packing  0.3-19.6 Influent TCE Concentration, ppmv   2-92 Propane feedrate, L/day/m³ packing   0-1000 Propane feed on interval, minutes 1Propane feed off interval, minutes   1-10 Propane feed duration,minutes/day   30-600 Propane feed concentration, volume %   0-1.8Propane concentration at start of TCE cycle, volume %   0-1.8 Propaneconcentration at end of TCE cycle, volume %   0-1.8 Presence of propanein TCE cycle, yes/no yes and no Extent of propane presence during TCEcycle, minutes   0-180 Extent of propane presence during TCE cycle, % ofTCE   0-100 cycle duration TCE degradation period, hours   1-6Closed-loop recycle period, hours   3-8 Operating Temperature, ° F.  40-106 Empty Bed Contact Time, minutes   7-54 TCE: recycle time ratio0.25-1 Oxygen concentration, volume %   15-21

[0185] Propane feed duration is the period of time in which continuousor intermittent propane flow was fed to the process.

[0186] Propane feed concentration is the concentration of propane in theinfluent air fed to the process.

[0187] Propane concentration at start of TCE cycle is the propaneconcentration in the recirculating internal process gas when theclosed-loop recycle period ends and the TCE degradation cycle begins.For the case of single-pass operation during the feeding cycle, it isthe propane concentration in the influent air fed to the biofilter.

[0188] Propane concentration at end of TCE cycle is the concentration inthe influent contaminated air being fed to the process when the TCEdegradation cycle ends and the closed-loop recycle feeding periodbegins. In preferred operation, this concentration is zero during theentire TCE degradation cycle to preclude to co-mingling of the primarysubstrate with the contaminant.

[0189] Presence of propane in TCE cycle refers to whether or not propaneis present internally in the process gas at the end of the propanefeeding cycle and at the beginning or during any part of the TCEdegradation cycle.

[0190] Extent of propane presence during TCE cycle in minutes is theduration in which propane is present during the TCE degradation cycle.This is preferably zero.

[0191] Extent of propane presence during TCE cycle in % of TCE cycle isthe percent of the total TCE degradation cycle time period in whichpropane is present during the TCE degradation cycle.

[0192] TCE degradation period is the period of time in which the processis operated in the TCE degradation cycle.

[0193] Closed-loop recycle period is the period of time in which theprocess is operated in the closed-loop (closed process system) recyclemode.

[0194] Operating temperature is the temperature of the air entering orleaving the biofilter. The minimum temperature listed in Table 1 is theminimum temperature of the influent air to the biofilter, and themaximum temperature is the maximum temperature of the effluent air fromthe biofilter. Generally, effluent temperatures were slightly higherthan influent temperatures.

[0195] Empty bed contact time (EBCT) is the period of time that theinfluent air would reside (residence time) in the biofilter packingduring the TCE degradation cycle if the biofilter contained no packing.This parameter is often used because the void space within differentpackings varies, and the EBCT yields a standard estimation of the totalvolume of the packing in the bed and thus is directly related to thesize (and cost) of the biofilter.

[0196] TCE:Recycle time ratio is the ratio of the TCE degradation periodto the closed-loop recycle period.

[0197] Oxygen concentration is the concentration of oxygen in theprocess gas leaving the biofilter during single-pass operation or theconcentration of oxygen in the internally recirculated process gasduring closed-loop recycle operation.

Example 3

[0198] Process performance and economics were dramatically improved bymodifying the Demonstration Unit to provide closed-loop recycle duringthe feeding cycle when the process was not receiving contaminated air.

[0199] For example:

[0200] propane use and cost decreased by an average of 96%

[0201] TCE degradation efficiency increased from an average of 47% to ashigh as 100%

[0202] TCE degradation rate increased by an average of nearly 600%

[0203] A return to single-pass operation during the feeding cyclereduced degradation efficiency from 99% to 37%. Obviously, propane useand cost is much lower with closed-loop recycle during feeding becauseall of the propane is kept within the system and consumed, whereas withsingle-pass operation during the feeding cycle, the vast majority of thepropane cannot be consumed as it passes once through the system and isreleased to the environment. Early attempts without closed-loop recycleto lower propane concentration or rate in an effort to increase theproportion of propane consumed and to decrease the proportion releasedto the environment resulted in lower biofilter performance levels.

[0204] Another more subtle but substantial advantage of the closed-looprecycle process scheme is that during the closed-loop feeding cycle, TCEadsorbed in the biofilter packing during the TCE degradation cycle isalso destroyed, so that when TCE is again introduced to the biofilterafter feeding, the level of adsorbed TCE in the packing is lower; thus,the packing has more capacity to remove TCE through a combination ofadsorption and degradation. Without the closed-loop recycle scheme, theTCE adsorbed in the packing and not yet destroyed by microorganismsduring the TCE degradation cycle was desorbed from the packing andreleased to the environment when the propane feeding cycle began. Intests without closed-loop recycle during feeding (single-pass mode),this resulted in higher effluent TCE concentrations during the propanefeeding cycle (when the process was not receiving TCE) than during theTCE cycle (when the process was receiving TCE), as is shown in FIG. 2.Thus, the apparent TCE degradation efficiency and rate during the TCEcycle appeared to be very high, but when the TCE released during thepropane feed cycle was included in the overall material balance oninfluent and effluent TCE for the system, the realized TCE degradationefficiency (and rate) was much lower. Some improvement in single-passfeeding was obtained in earlier bench-scale work as shown in FIG. 3 bydelaying the start of propane feed and/or by ceasing propane feed earlyduring the feeding cycle, to reduce or eliminate presence of propane inthe system during the TCE cycle and to reduce or eliminate adsorbed TCEduring propane feeding. However, the improvement was insufficient andstill wasted propane, and it was recognized that a change in processscheme was necessary to: (1) eliminate TCE emissions during propanefeeding and (2) consume all propane fed to the biofilter. In earlierbench-scale work, improvement through such a scheme during part of thepropane feeding cycle (TCE-off cycle) was verified as shown in FIG. 4.However, what was recognized as essential was a process scheme tocompletely eliminate all TCE emissions during the full propane feedingcycle and to ensure complete consumption and no waste of propane, asshown in FIG. 5 after implementation of closed-loop recycle in theDemonstration Unit.

[0205] The improvement due to the closed-loop recycle scheme became moreapparent earlier in the Demonstration than was foreseen, so the decisionwas made to implement a simpler form of recycle than had first beenenvisioned. Originally, it was envisioned that closed-loop recycleduring feeding would involve control loops (added cost) to vent someprocess gas and add makeup air to provide sufficient oxygen, to preventbuild up of carbon dioxide, and to add propane and maintain propaneconcentration at optimum levels until near the end of the feed cycle,when propane feed would be discontinued and the microorganisms would beallowed to complete consumption of all available propane before TCE wasreintroduced. Presence of propane during introduction of TCE results inlow performance because the microorganisms consume propane in favordegrading TCE, and adsorbed TCE is desorbed and emitted to theenvironment. The simpler form of recycle provided only for charging ofthe closed biofilter system with propane and then recirculating of thein-system process gas until the propane was depleted and did not providefor the propane and oxygen control loops and the venting and make upstreams earlier envisioned as necessary. The simpler scheme wasinexpensive. It was believed at the time that the simpler scheme wouldnot be optimal but would show whether or not the scheme was effective.Scientific wisdom indicates that this simpler closed-loop recycle schemewould eventually result in process failure because when the closedbiofilter system is charged with propane up to the safe concentrationand the process gas is then allowed to recirculate in the closed systemuntil all of the propane is consumed, the oxygen demand that exists forthe propane alone dictates that the oxygen supply should be depleted,resulting in the death of the aerobic microorganisms. Unexpectedly, itwas discovered that the oxygen levels within the closed system werereduced only slightly, which defies conventional scientific wisdomconcerning the function of these aerobic microorganisms, and the simplerrecycle system dramatically improved performance as shown in FIG. 5.

Example 4

[0206]FIG. 6 shows that the influent TCE load had a significant butpredictable effect on TCE degradation rate.

[0207] However, the degradation rate alone does not fully describebiofilter performance because it does not take into account thedegradation efficiency, which is a measure of the proportion of theinfluent TCE that the biofilter destroys. Degradation efficiency isdisplayed along with degradation rate in FIG. 7 and can be seen to varyinversely with degradation rate. In other words, as the rate of TCE fedto the biofilter increases, the degradation efficiency decreases and thedegradation rate increases. Increasing the TCE degradation efficiencyrequirement decreases the TCE load and degradation rate that thebiofilter is capable of handling and therefore increases the size of thebiofilter. For example, a TCE biofilter could be designed to achieve ahigh degradation rate but with a degradation efficiency of only 50%,which, depending on site requirements, may or may not be acceptable. Ifit is required for a specific application that a biofilter system meetonly a specific effluent TCE concentration, and if a 50% removalefficiency will meet this requirement, designing the biofilter (andmanipulating the waste stream if applicable) to maximize degradationrate would be most cost effective by minimizing biofilter size.

Example 5

[0208] It was originally envisioned that a TCE Biofilter process wouldconsist of two biofilters—one receiving the waste stream while the otherwas in closed-loop recycle feeding mode. When the feeding cycle wascomplete, the freshly fed biofilter would then begin to receive thewaste stream and the other biofilter would be set to begin theclosed-loop recycle feeding mode. During the course of theDemonstration, it was observed that when testing shorter EBCTs in aneffort to decrease biofilter size, the effluent TCE concentration wouldat some point during the TCE cycle begin to increase more rapidly asshown in FIG. 8, indicating “break through” of the TCE waste stream. Atthat point, the adsorption and degradation capacity of thebiodegradation media (packing) had been surpassed. In other words, up tothat point, adsorption and degradation of TCE within the packing hadprevented high effluent TCE concentrations because the waste streamtrain had not yet reached the top of the packing, but as the TCE airstream traveled through the biofilter packing and reached the top of thepacking, higher effluent concentrations developed due to break through,because the packing's adsorption and degradation rate capacities atthose process conditions were less than the rate of TCE being fed to thebiofilter.

[0209] Results suggested that the degradation efficiency could beimproved and the effluent TCE concentration could be reduced byshortening the length of the TCE degradation cycle relative to theclosed-loop recycle feeding period. It was reasoned that this wouldprevent breakthrough during the TCE cycle, allow more time for microbialdegradation of TCE during closed-loop recycle, and provide moreadsorption capacity and TCE degradation enzymes for the next TCE cycle.Of course, shortening the TCE cycle relative to the recycle feedingperiod was expected to require more than two biofilters. For example,with a TCE degradation period of 2 hours and a closed-loop recyclefeeding period of 4 hours, three biofilters would be needed so that onebiofilter would always be available for receiving the continuous wastestream—that is, if the waste stream is continuous. In some applicationssuch as solvent degreasing, the gaseous waste stream is only continuousat certain times of the day. In such situations, it was reasoned thatthere might be a need for only one biofilter, if the time available forfeeding and degradation of adsorbed TCE was sufficient to meet siteperformance requirements during the intermittent periods of flow of thewaste stream to the biofilter. In addition, since the currentgroundwater air stripping systems at the decontamination site have sumpswhich collect the groundwater for pumping to the air strippers, webelieved that only a single biofilter would be required if the existingor designed sump capacity would allow a surge volume (storage ofincoming groundwater) that would allow pumping of the groundwater to thestrippers at twice the normal continuous groundwater flow rate for onlyhalf of the time. For example, if incoming groundwater at 20 gallons perminute could be allowed to flow into a sump or other collection vesseland stored for 4 hours (total of 4800 gallons) during the singlebiofilter's recycle feed period, the groundwater could then be pumped toan air stripper at 40 gallons per minute for the next 4 hours (total of9600 gallons to remove the stored and the incoming water) and theresulting contaminated air stream could be fed to the biofilter for the4-hour TCE cycle. If the existing stripper parameters or designparameters of a new stripper are such that the 40-gallon-per-minutewater flow rate could produce a contaminated air stream of the samevolumetric flow rate but at twice the concentration, rather than twicethe air rate at the same concentration, the design size and cost of thebiofilter generally would be lower than a two-biofilter system forcontinuous air stripping. For a given TCE load (dictated by site orapplication), the biofilter design size and cost and the cost per unitof pollutant destroyed generally decreases with increase in theconcentration and with decrease in the flow rate of the waste stream.Thus, the biofilter capital and operating costs would be lower foroperating one biofilter instead of two. For an application in which thewaste stream is already in the gas phase and flow is continuous, asingle biofilter system would still be possible using an air compressorand a pressurized air storage tank to store the waste gas during therecycle feeding period and then to feed the contaminated air to thebiofilter at a higher flow rate only during the TCE cycle.

[0210] Indeed, decreasing the TCE cycle time relative to the closed-looprecycle feeding time in an attempt to avoid TCE break through yieldedresults we expected, as shown in Table 2. Decreasing the TCE:recycletime ratio increases the water or gas storage capacity required, but itincreased the degradation efficiency and decreased the effluent TCEconcentration, albeit at the expense of degradation rate, whichdecreased. A decrease in degradation rate would normally indicate anincrease in the volume (size and cost) of the biofilter for asite/application-specific air rate and concentration. However, this doesnot take into account the advantage in decreased biofilter size and costthat can be achieved by manipulating the waste stream so as to produce alower volume, higher concentration air stream for a given TCE load(constant for site), if this flexibility exists. TABLE 2 Effect of TCE:Recycle Time Ratio Average TCE Average Average TCE TCE: RecycleDegradation Effluent TCE Degradation Time Ratio, Efficiency,Concentration, Rate, g/day/m³ hr:hr % ppmv packing 4:4 69 17.8 9.8 4:884 4.5 3.8 2:4 98 0.4 3.1 2:6 98 0.6 2.7 1:3 98 0.2 1.0

Example 6

[0211] In order for those skilled in the art to better understand theconcepts of the present invention, the following working examples forboth cometabolic processes and directly metabolic processes are herebygiven and explained as specific examples of actual process operatingparameters and the resulting process performance achieved during fieldoperation of the Demonstration Unit as described in detail in Examples 1and 2. These operating parameters are simply specific examples of theprocess parameters for cometabolic or directly metabolic processes thatwere used during operation of the Demonstration Unit of Example 1 toachieve a specific process performance and are given here simply as onespecific example of the process performance obtained while practicing aspecific set of process operating conditions and are in no way intendedto limit the scope and spirit of this invention to those particularvalues. The process equipment and operation methods used to achieve theprocess performance results of the following specific example are alsodescribed in detail in Example 1. The specific process operatingparameters and the resulting process performance achieved are shown inthe tables below: Specific Process Parameter Values and ResultingProcess Performance Values for TCE Cometabolic Degradation via Propaneas Primary Substrate PROCESS PARAMETERS Closed-loop recycle system, yesor no yes Influent TCE load, g/day/m³ packing 6.4 Influent TCEConcentration, ppmv 37 Propane feed rate, L gas/day 1875 Propane feed oninterval, minutes 1 Propane feed off interval, minutes 1 Propane feedduration, minutes/day 240 Propane feed concentration, volume %   0-1.5Propane concentration at start of TCE cycle, volume % 0 Propaneconcentration at end of TCE cycle, volume % 0 Presence of propane in TCEcycle, yes/no no Extent of propane presence during TCE cycle,minutes/day 0 Extent of propane presence during TCE cycle, % of 0 TCEcycle duration TCE degradation period, hours 2 Closed-loop recycleperiod, hours 4 Operating temperature, ° F. 82 TCE Cycle Empty bedcontact time, minutes 15 TCE: recycle time ratio (2 hours:4 hours) 0.5Oxygen concentration, volume % 18-21 PROCESS PERFORMANCE DegradationEfficiency, % 97 Degradation Rate, g/day/m³ packing 6.2 Effluent TCEConcentration, ppmv 0.9

[0212] Specific Process Parameter Values and Resulting ProcessPerformance Values for Degradation of Propane (or Other AmenableCompounds) via Direct Metabolism PROCESS PARAMETERS Closed-loop recyclesystem, yes or no yes Propane feed rate, L gas/day 1875 Propane feedload, g/day 3374 Propane feed on interval, minutes 1 Propane feed offinterval, minutes 1 Propane feed duration, minutes/day 240 Propane feedconcentration, volume %   0-1.5 Propane feed concentration, ppmv   0-15,000 Closed-loop recycle period, minutes 240 Closed-loop emptybed contact time, minutes 4 Open-loop fresh air single pass purgeperiod, 4 minutes Open-loop fresh air single pass empty bed 4 contacttime, minutes Operating temperature, °0 F. 82 Oxygen concentration,volume % 18-21 PROCESS PERFORMANCE Degradation Efficiency, % 100Degradation Rate, g/day 3374 Effluent Propane Concentration, ppmv 0

[0213] Those of ordinary skill in the art will appreciate that thevalues in the above tables for cometabolism and direct metabolismprocesses are within the operating ranges of this invention but are notnecessarily optimum values. Further, those of ordinary skill in the artwill appreciate that the values in the above table for direct metabolismof propane can be varied to higher process flow rates, concentrations,and influent pollutant loads with resulting higher process efficienciesand degradation rates for a wide variety of other pollutants that can bebiodegraded by direct metabolism more easily than propane, such asalcohols, esters, ethers, ketones, aromatics, and so forth, asdescribed, supra.

Example 7

[0214] The processes of the present invention, particularly fordecontaminating gaseous waste streams, can also be operated without anypacking or support media for the microorganisms. Using this processscheme, the microorganisms are contacted with the contaminated stream byrecirculating a fluid nutrient-microorganism suspension spray throughthe biofilter or bioreactor on a closed-loop basis. This process schemeis more advantageous for use with a wide variety of pollutants that havehigher water solubilities and lower gas-liquid partition coefficients(Henry's Law Constants), i.e. that have greater tendency to transfer toand/or remain in the liquid phase, where biodegradation occurs. Suchpollutants include a wide variety of alcohols, ketones, esters, ethers,ammonia, hydrogen sulfide, and many others. The fluidnutrient-microorganism suspension is recirculated through the processvia spray nozzles at rates sufficient to obtain a spray or mist of themicroorganism suspension so as to produce more liquid surface area fortransfer of the pollutants from gas to liquid phase, as will beappreciated by those or ordinary skill in the art. The results obtainedusing this process scheme are similar to those obtained and shown in thetables of Example 6, supra.

Invention Parameters

[0215] After sifting and winnowing through the data, supra, as well asother results and operations of our new and novel processes, includingmethods and means for the effecting thereof, the process operatingparameters for carrying out our invention for cometabolism processes aresummarized in Table 4, below, and for carrying out our invention fordirect metabolism processes are summarized in Table 5, below, with theircorresponding operating range limits for the present invention. Theprocess parameters can be varied in an empirical fashion to achieve themaximum process performance and economics as desired in accordance withthe present invention. At present, we believe the significant processparameters are those shown in Tables 4 and 5 based on the results of theDemonstration Unit described in the Examples. We further believe thatthe process parameters of the present invention can be varied within theranges shown in Tables 4 and 5. Explanation of the process operatingparameters in Table 4 were described in Example 2 for Table 1, supra. Inthe Demonstration Unit described in the Examples, TCE and propane wereused as the contaminant and primary substrate, respectively, and areshown as invention process parameters in Table 4 for illustrativepurposes and are not intended to be limiting as the contaminant andprimary substrate for the purposes of the present invention, as theprocesses of the present invention may be practiced with othercontaminants and other primary substrates as discussed, supra, or withcontaminants which can be directly metabolized as a food and growthsource by naturally occurring microorganisms as explained, supra,without the need for a cometabolism step, as shown in Table 5. Forpollutants capable of degradation by direct metabolism, the cometabolismcycle (e.g. the TCE cycle in Table 4) is eliminated, and most values forpropane in Table 4 correspond to pollutants degradable by directmetabolism shown in Table 5, such as benzene, toluene, xylenes, methylethyl ketone and other ketones, methyl alcohol and other alcohols, butylacetate and other esters, methyl tertiary butyl ether and other ethers,ammonia, hydrogen sulfide, carbon disulfide, and a wide variety ofpollutants or other undesirable compounds that can be directlymetabolized by naturally occurring microorganisms.

[0216] For some process variables in Tables 4 an 5, the operating rangesgiven in the provisional application shown in Table 6 below weresomewhat narrower than given in the non-provisional application of thepresent invention. However, we believe that, while these narrowerprocess parameter ranges in Table 6 are preferred operating ranges, themost preferred operating ranges are given in Tables 4 and 5. TABLE 4Process Parameters and Operating Ranges for Cometabolism ProcessesClosed-loop recycle system, yes or no yes or no Influent TCE (or othertarget pollutant) load,    0-1000 g/day/m³ packing Influent TCE (orother target pollutant) concentration, 0.001-10,000 ppmv (in gas stream)Propane or other food source feed rate, L  0.1-20,000 gas/day/m³ packingPropane feed on interval, minutes  0.01-1440 Propane feed off interval,minutes  0.01-1440 Propane feed duration, minutes/day  0.01-1440 Propanefeed concentration, volume %    0-2.1 Propane concentration at start ofTCE cycle,    0-2.1 volume % Propane concentration at end of TCE cycle,volume %    0-2.1 Presence of propane in TCE cycle, yes/no yes or noExtent of propane presence during TCE cycle,    0-1440 minutes/dayExtent of propane presence during TCE cycle,    0-100 % of TCE cycleduration TCE degradation period, hours  0.02-720 Closed-loop recycleperiod, hours  0.02-720 Operating temperature, ° F.   33-140 Empty bedcontact time, minutes  0.1-1440 TCE: recycle time ratio 0.001-1000Oxygen concentration, volume %    0-22

[0217] TABLE 5 Process Parameters and Operating Ranges for DirectMetabolism Processes Closed-loop recycle system, yes or no yes or noPollutant load, g/day/m³ packing    0-50,000 Pollutant concentration,ppmv (in gas stream) 0.001-20,000 Pollutant feed on interval, minutes 0.01-1440 Pollutant feed off interval, minutes  0.01-1440 Pollutantfeed duration, minutes/day  0.01-1440 Closed-loop recycle period, hours 0.02-720 Operating temperature, ° F.   33-140 Empty bed contact time,minutes  0.02-1440 Oxygen concentration, volume %    0-22

[0218] TABLE 6 Process Parameters and Operating Ranges in ProvisionalApplication Closed-system recycle, yes or no yes or no Influent TCEload, g/day/m³ packing    0-400 Influent TCE Concentration, ppmv0.001-10,000 Propane feed rate, L/day/m³ packing  0.1-20,000 Propanefeed on interval, minutes  0.01-1440 Propane feed off interval, minutes 0.01-1440 Propane feed duration, minutes/day  0.01-1440 Propane feedconcentration, volume %    0-2.1 Propane concentration at start of TCEcycle, volume %    0-2.1 Propane concentration at end of TCE cycle,volume %    0-2.1 Presence of propane in TCE cycle, yes/no yes or noExtent of propane presence during TCE cycle,    0-1440 minutes/dayExtent of propane presence during TCE cycle, % of TCE    0-100 cycleduration TCE degradation period, hours  0.02-720 Closed-loop recycleperiod, hours  0.02-720 Operating Temperature, ° F.   33-140 Residencetime (empty bed contact time), minutes    1-1440 TCE: recycle time ratio0.001-1000 Oxygen concentration, volume %    0-22

[0219] In addition, and as previously discussed, supra, the processes ofthe present invention may be applied to detoxification of liquidcontaminated streams by contaminant degradation directly in thecontaminated liquid, as discussed in DESCRIPTION OF THE DRAWINGS, supra.Any contaminants in gas phase must first be transferred to liquid phaseor dissolved into the liquid phase on or in the microorganisms beforebiodegradation or enzymatic degradation can occur. Therefore, if thecontaminants already exist in liquid phase, there is no purpose in firsttransferring the contaminants to the gas phase, as was practiced by theair stripping step in the Demonstration Unit in the EXAMPLES, supra,when the resulting gas phase contaminants will simply have to betransferred back into the liquid phase on or into the microorganisms fordegradation to occur. Following are some other important considerationsconcerning Table 4 and the practicing of the present invention.

[0220] Although temperature was not a controlled parameter in theDemonstration Unit, temperature is an important parameter and can befreely varied by one of ordinary skill in the art to optimizeperformance of the process so long as the microorganisms are not harmed.For example, the Demonstration Unit influent/effluent temperature rangewas 42 to 106° F., and we believe that temperatures substantially belowand substantially above this range can be used so long as theconsiderations earlier discussed are heeded.

[0221] “Influent TCE load” is listed as zero (0) for those periods whenthe processes are in the primary substrate feeding cycle. We wish tomake it clear that we believe the processes of the present inventionfunction best when no TCE (or other degradable contaminant) is presentduring the primary substrate feeding cycle and no primary substrate ispresent during the TCE degradation cycle. However, the presence of someTCE in the feed cycle and some primary substrate in the TCE degradationcycle are not excluded, rather, this simply renders the presentinvention less efficient and is currently not preferred.

[0222] It is our current belief that TCE parameters which have any zero(0) value in Table 4 are best kept to a value on the order of about 0.01(preferably less, of course), though the units in Table 4 will vary. Wepicked this value rather arbitrarily to express our belief that theabsence of TCE in the propane feed cycle and the absence of propaneduring the TCE degradation cycle provide optimum process performance andeconomics.

[0223] With respect to “Influent TCE Concentration”, we set this rangerather broad to include what we expect would be values of commercialinterest. At a concentration of less than about 0.001 ppmv, the streamis dilute to the extent that its treatment would probably beeconomically impractical. On the other hand, with respect to TCEconcentration values greater than about 10,000, we believe that the samewill seldom be encountered in the type of environments where we believethe process of the present invention will be most useful. However, intheory, operation at the extremes is feasible.

[0224] Obviously “Propane feed rate” will be influenced by other processparameters and operating ranges, and this should be apparent to one ofordinary skill in the art.

[0225] “Propane feed on interval” and “Propane feed off interval”reflect times during the propane feed cycle when propane is fed to thebiofilter and when propane is not fed to the biofilter. These termsconvert to six seconds to one day and reflect what we believe shouldinclude most practical operating times, but there is no theoreticalreason of which we are aware why shorter and longer times could not beused given the mechanism of the process of the present invention.However, working at the extremes may not be economically desirable.Similar remarks apply to “Propane feed duration”.

[0226] With respect to “Propane feed concentration” (volume % based onthe carrier stream, typically air for gas phase operations, hereafterthe same for all volume % values), the 0 volume % value is what webelieve to be the most desirable value—the absence of propane—during theTCE degradation cycle. The upper limit is set by a very practicalconsideration, the lower explosive limit (LEL). The upper limit can varydepending on the primary substrate and is set by safety factors. Forexample, for propane the LEL given in various sources is on the order of2.2-2.4%, and for safety purposes the concentrations used in our workhave typically been set to a maximum of 1.5%. Similar remarks apply tothe “Propane concentration at start of TCE cycle” and “Propaneconcentration at end of TCE cycle”.

[0227] With respect to “Presence of propane in TCE cycle, yes/no”,“yes/no” refers to whether or not propane is present at the beginning orduring the TCE cycle.

[0228] There are two recitations for “Extent of propane presence duringTCE cycle”, one in “minutes” and one in “%” of TCE cycle duration. Fromthe earlier discussion, it will be apparent that we prefer that there beno propane present during the TCE degradation cycle, but again thepresence of some propane is not excluded, it being understood that thegreater the amount of propane present the less efficient the process ofthe present invention becomes.

[0229] The “TCE degradation period” simply refers to what we currentlybelieve to be the probable minimum time and maximum time that TCEdegradation will be conducted for most practical processes. Similarremarks apply to “Closed-loop recycle”.

[0230] With respect to “Operating Temperature”, generally the higher thetemperature the more efficient the biofilter process of the presentinvention.

[0231] With respect to “Empty bed contact time” (EBCT) we selected thisparameter since it is commonly used in the biofilter/bioreactor art as ameans to characterize the effective residence time without being limitedto packing of any particular size. For example, obviously spheres 1″ indiameter will provide a different void volume (free space) thanfine-grain sand when used in a biofilter/bioreactor. As is the case withother parameters, we selected EBCT to include what we think will bethose most commonly used on a commercial basis.

[0232] With respect to “TCE:recycle time ratio”, this reflects the TCEdegradation cycle time period with respect to the feed cycle timeperiod. Although it is unit-less, time will always be the same for eachcycle (minutes, hours, etc.) so that the ratio has meaning. We selecteda rather broad range for this ratio since it can vary greatly dependingupon other process parameters chosen and process performance required.It is believed that one of ordinary skill in the art can easilyappreciate how to balance the various factors involved in the processesof the present invention to select an appropriate TCE:recycle time ratiobased on the process performance and economics required.

[0233] Finally, with respect to “Oxygen concentration”, we set the lowerlimit as 0 to include the possibility of microsites of anaerobicbacteria existing in the biofilter. As a practical matter, however, wecurrently do not see an oxygen level of less than 0.001 volume % or even0.01 volume % to be of commercial importance. We set the upper limit toapproximate the oxygen concentration in air which we view as thepractical supplier of oxygen to the microorganisms of the presentinvention. If one were to accept cost/dangers of increased oxygenlevels, we see no reason why such increased oxygen levels could not beused.

[0234] We selected the mixture of composted poultry litter, pine bark,chopped kenaf, and pelletized dolomitic limestone for the biofilterpacking primarily because of its low cost and its availability. Needlessto say, for the reasons discussed herein, the exact nature of thepacking is not overly important so long as process gases or liquids canflow through the packing without obstruction. The exact size of thevarious components of the mixture we used in the demonstration unit isnot important so long as the contaminated stream and primary substratestream can flow through the packing and contact the microorganismstherein.

[0235] Usually, the pH of the biodegradation media of the presentinvention is simply set within the neutral range of approximately pH of5 to 8 since the microorganism used thrive within this range. The pH canan easily be set or adjusted by one of ordinary skill in the art.

[0236] Moisture level in the biodegradation media of the presentinvention is simply set so the microorganisms are healthy. There is noneed to add extra water if the amount present is sufficient for thispurpose. This proper moisture level can easily be determined andcontrolled by one of ordinary skill in the art.

[0237] Packing particle size and depth are set to ensure a fairly evenflow of the process streams through the packing without excessiveresistance to flow. The more even the flow the better, but as one ofordinary skill in the art will appreciate with respect to many aspectsof the present invention, this is a matter of degree, and one simplyloses process efficiency with a more uneven flow through the packing.

[0238] While we have shown and described particular embodiments of ourinvention, modifications and variations thereof will occur to thoseskilled in the art. We wish it to be understood, therefore, that theappended claims are intended to cover such modifications and variationswhich are within the true spirit and scope of our invention.

What is claimed is:
 1. A process for the treatment of a fluid toaerobically degrade a compound contained in the fluid by contacting thefluid with a microorganism, whereby the microorganisms aerobicallydegrade the compound, the process comprising: (a) contacting the fluidwith the microorganism where the fluid contains a start pass undesiredamount of the compound in the fluid for a period of time and underconditions such that the microorganism will act on the compound andaerobically degrade the compound and reduce the amount of the compoundin the fluid to an end pass lesser undesired amount of the compound inthe fluid as compared to the start pass undesired amount of the compoundin the fluid; (b) removing the fluid containing the compound at the endpass lesser desired amount of the compound in the fluid from thecontacting with the microorganism; (c) circulating the fluid containingthe compound at the end pass lesser desired amount of the compound inthe fluid in a closed loop substantially closed to the environmentexterior to the process; (d) again contacting the fluid with themicroorganism where the fluid initially contains the end pass lesserdesired amount of the compound in the fluid for a period of time andunder conditions such that the microorganism will act on the compoundand aerobically degrade the compound and the amount of the compound inthe fluid is reduced to a lower end pass lesser desired amount of thecompound as compared to the end pass lesser desired amount of thecompound in the fluid; (e) repeating steps (b), (c) and (d) until theamount of the compound in the fluid is reduced to a final end passundesired amount of the compound in the fluid which is less than thelast end pass lesser desired amount of the compound in the fluid toundergo the again contacting of step (d); (f) stopping the process. 2.The process of claim 1, which is a direct metabolic process whichconsists essentially of steps (a) to (f).
 3. The process of claim 2,which is conducted in a biofilter system.
 4. The process of claim 2,which is conducted in a bioreactor system.
 5. The process of claim 1,which is a cometabolic process wherein between steps (e) and (f) thecontacting of the fluid containing the compound is temporarilydiscontinued and in the substantial absence of the fluid containing thecompound a gas or liquid containing a primary substrate for themicroorganism which is contacted with the microorganism for a timesufficient and under conditions effective for the primary substrate tofeed the microorganism and actuate enzymes, which enzymes aerobicallydegrade the compound.
 6. The process of claim 5, which is conducted in abiofilter system.
 7. The process of claim 5, which is conducted in abioreactor system.
 8. A process for the cometabolic degradation of acontaminant, the process comprising: (a) separation of a primarysubstrate stream and a contaminant stream into separate and discreteprocess streams used in separate and discrete process cycles, a primarysubstrate feeding cycle and a contaminant degradation cycle, such thatthe primary substrate stream is fed to the process part of the time tofeed the microorganisms and activate enzymes which effect contaminantdegradation and the contaminant stream is fed to the process part of thetime to effect cometabolic degradation of the contaminant as it passesthrough the process; and (b) substantially eliminating the flow andpresence of the contaminant stream in the process during the primarysubstrate feeding cycle and substantially eliminating the flow andpresence of the primary substrate stream in the process during thecontaminant degradation cycle to substantially eliminate co-mingling orsimultaneous presence of the primary substrate and the contaminantwithin the process; and (c) controlling the periods of time allowed forflow of the primary substrate stream and flow of the contaminant streamand the periods of time allowed for cycles of the process; and (d)employing closed-loop recycle, such that during said closed-loop recyclethe process is completely enclosed and separated from the outsideatmosphere with substantially no net process flows entering or leavingthe process and with internal process gases and/or liquids continuouslyrecycled through the enclosed process, said closed-loop recycle beingused during the primary substrate feeding cycle, the closed-loop recycleoperation effecting consumption of substantially all of the primarysubstrate fed to the process during said cycle and effecting thesubstantial elimination of any release of primary substrate orcontaminant from the processes during said cycle, wherein degradation ofthe contaminant during said cycle where the contaminant exists inadsorbed form within the process or in residual process gas resultingfrom a prior contaminant degradation cycle is also accomplished.
 9. Theprocess of claim 1 which is a direct metabolic or cometabolic process,wherein the microbial consortiums are self-optimizing such that theprocesses force the adaptation, dominance, and maintenance of theoptimal microbial types, mixtures, and populations within the processesthat effect the most efficient and economical degradation of the targetcontaminants as they occur naturally in the environments or other wastestreams, without the need for replenishing the processes with pure,externally grown microbial strains and without the need for the initialinoculation of the processes with specially cultured, externally grownstrains of microorganisms, and rather, allowing no initial inoculationor the initial inoculation of the processes with the waste stream to bedetoxified or soil sediments, water, or other natural media collectedfrom widespread environments that are contaminated with site-specificpollutants targeted for detoxification, and that therefore containdiverse, wild-type indigenous microorganisms which have adapted topresence of such contaminants.
 10. The process of claim 1 which is adirect metabolic or cometabolic process , wherein the mode of operationis continuous, batch, single-pass, recycled, or a combination thereof.11. The process of claim 1 which is a direct metabolic or cometabolicprocess, wherein the contaminated streams fed to the processes are inthe form of gases and/or liquids from contaminated groundwater, solventdegreasing or soil vapor extraction.
 12. The process of claim 1 which isa direct metabolic or cometabolic process, wherein the said undesirablecompounds are VOCs, and/or SVOCs.
 13. The process of claim 1 which is acometabolic process wherein the primary substrate is an alkane, aromaticor phenolic compound.
 14. The process of claim 1 which is a directmetabolic or cometabolic process, wherein the contaminants arechloroethylenes.
 15. The process of claim 1 which is a direct metabolicor cometabolic process, utilizing single or multiple biodegradationreactors.
 16. The process of claim 1 which is a direct metabolic orcometabolic process, wherein a microbial support or packing media isused which is a natural and/or synthetic material.
 17. The process ofclaim 16 which is a direct metabolic or cometabolic process, wherein themicrobial support or packing media is a sorbent material.
 18. Theprocess of claim 16 which is a direct metabolic or cometabolic process,wherein the microbial support or packing media comprises activatedcarbon.
 19. The process of claim 1 which is a direct metabolic orcometabolic process, wherein a microbial support or packing media is notused, the microorganisms are not immobilized on or in a microbialsupport or packing media, and said microorganisms are contained in aliquid that is sprayed into the process and recirculated within theprocess.